Here’s the latest on COVID-19 vaccines

Everything you need to know about the COVID-19 vaccines—from their safety and efficacy to the global vaccine rollout.

Editor’s note: As of November 2021, this COVID-19 vaccine tracker is no longer being updated. Stay up-to-date on the latest vaccine developments and other COVID-19 news here.

COVID-19 vaccines have reached consumers in record time. Though the process can typically take 10 to 15 years, the U.S. Food and Drug Administration has granted emergency authorization to vaccines made by Pfizer, Moderna, and Johnson & Johnson in less than a year. Before now, the fastest-ever vaccine—for mumps—took four years to develop in the 1960s.

Fortunately, scientists had started working on the seeds of these vaccines long before COVID-19 emerged–teams were doing breakthrough work on mRNA technology for 12 years before the pandemic, and a global push to make clinical trials for COVID-19 more efficient helped ensure the world had safe, effective drugs in record time.

Even after a vaccine is authorized or fully licensed, it faces potential roadblocks when it comes to scaling up production and distribution, which also includes deciding which populations should get it first—and at what cost.

Here’s everything you need to know—including primers on how vaccines and clinical trials work, the latest news on vaccine distribution and safety, and a detailed breakdown of the early candidates.

Vaccines and clinical trials

Vaccines go through a three-stage clinical trial process that’s required before they are sent to regulatory agencies for approval. Given the urgent need, some vaccine developers compressed the clinical process for SARS-CoV-2 by running trial phases simultaneously.

The COVID-19 candidates, like all vaccines, essentially aim to instruct the immune system to mount a defense, which is sometimes stronger than what would be provided through natural infection and comes with fewer health consequences.

To do so, traditional vaccines use the whole coronavirus, but in a killed or weakened state. Others use only part of the virus—whether a protein or a fragment. Some transfer the instructions for coronavirus proteins into an unrelated virus that is unlikely or even incapable of causing disease. Finally, cutting-edge vaccines under development rely on deploying pieces of the coronavirus’s genetic material, enabling our cells to temporarily make coronavirus proteins needed to stimulate our immune systems. (Find out more about vaccines and how they work.)

U.S. vaccine rollout

Three COVID-19 vaccines are available for use in the United States. U.S. regulators have approved Pfizer’s vaccine for adults and authorized it for emergency use in children and adolescents ages five to 17. The U.S. has also granted emergency use authorization to administer the Moderna and Johnson & Johnson vaccines to adults.

Some populations in the country are eligible for booster doses. Anyone who received a Johnson & Johnson single-shot jab can get a second dose after at least two months. People who received the Pfizer and Moderna vaccines are eligible for a third dose after six months if they are over 65 or have an underlying condition that makes them more susceptible to severe COVID-19. People whose institutional or occupational settings put them at high risk of exposure to the coronavirus may also get a booster shot. U.S. regulators have permitted people to mix-and-match their jabs in the wake of data suggesting that people who originally received the Johnson & Johnson vaccine are protected by a booster dose of the Pfizer or Moderna vaccines.

U.S. regulators have also recommended a third dose of the Pfizer and Moderna vaccines for people with compromised immune systems. This extra dose is considered part of their primary vaccination series; CDC guidance suggests that immunocompromised people will be able to get a fourth booster dose six months after completing the primary series.

Global vaccine rollout

The World Health Organization is coordinating global efforts to administer vaccines, with an eye toward delivering two billion doses by the end of 2021. It is leading an initiative through the COVAX Facility to ensure that all countries have equitable access. The WHO has approved the Pfizer-BioNTech, AstraZeneca-Oxford, Johnson & Johnson, Moderna, Sinopharm, Sinovac, and Bharat Biotech vaccines for emergency use.

Vaccine safety

On July 13, the U.S. Food and Drug Administration added a warning label to Johnson & Johnson’s vaccine after it was linked to rare cases of Guillain-Barré Syndrome, an autoimmune disorder that can lead to paralysis. There have been 100 preliminary reports of the syndrome among the approximately 12.5 million people who have received the vaccine. The FDA said that the benefits of receiving the vaccine outweigh the risks.

The FDA has also added a warning label to the Pfizer and Moderna vaccines about rare cases of heart inflammation in adolescents and young adults. The move came after the CDC’s Advisory Committee on Immunization Practices announced that it has identified more than 300 cases of myocarditis and pericarditis that it acknowledged are likely linked to the vaccines. The agency says these cases are rare but higher than expected. It also said the benefits of the shots outweigh the risks.

 In April, the European Medicines Agency issued statements saying that unusual blood clots should be listed as a very rare but possible side effect of both the AstraZeneca and Johnson & Johnson vaccines. In a review of 86 reported cases related to the AstraZeneca vaccine, the EMA’s safety committee found a potential link between it and the clots, with most known cases occurring in women under age 60 within two weeks of receiving the first dose. The EMA stressed that the odds of developing a clot after vaccination are extremely low, and that the benefits of getting vaccinated outweigh the risks. They also recommend that people seek immediate medical attention if they experience symptoms related to clotting, including persistent pain, shortness of breath, and headaches or blurred vision.

On August 27, a study published in the British Medical Journal affirmed the EMA’s risk-benefit analysis, showing that there’s a much higher risk of developing blood clots after SARS-CoV-2 infection than after immunization with the AstraZeneca or Pfizer vaccines.

On August 11, the CDC officially recommended that people who are pregnant, breastfeeding, or may become pregnant get a COVID-19 vaccine. A new analysis of data from the vaccine rollout found no increased risk of miscarriage among people who received an mRNA vaccine before 20 weeks of pregnancy. Earlier studies also showed that the vaccine is safe later in pregnancy as well—for both pregnant people and their babies. The CDC emphasized the urgency of vaccination among these groups in a health alert issued on September 29, reporting new data showing a rise in COVID-19-related deaths among pregnant people.

Vaccine prospects

Here are some of the vaccines that have made it to phase three and beyond:

Pfizer

Name: BNT162b2 

Who: One of the world’s largest pharmaceutical companies, based in New York, in collaboration with German biotech company BioNTech.

What: A nucleic-acid vaccine that requires two doses taken 21 days apart. 

Approval status: On December 2, the U.K. became the first Western country to approve any COVID-19 vaccine when it authorized the Pfizer-BioNTech candidate—making the drug the first mRNA vaccine in history allowed for human use. The FDA granted emergency use authorization to this vaccine on December 11, 2020, and fully approved it on August 23, 2021. The vaccine has also been granted emergency approval in Canada, the European Union, and other countries.

U.S. regulators have also approved Pfizer’s vaccine for emergency use in children and adolescents ages five to 15. U.K. regulators have also approved this vaccine for use among adolescents ages 12 to 15, while the European Union granted conditional authorization.

As of September 24 U.S. regulators granted emergency use authorization of a third dose of Pfizer’s vaccine—but only for certain subgroups of the national population, including older people and those with underlying conditions that put them at higher risk of disease and for people in occupational or institutional settings that put them at high risk of infection, such as health-care workers and teachers.

Distribution: Globally, Pfizer expects to be able to produce up to 1.3 billion doses by the end of 2021. Questions have been raised over the vaccine’s storage, which requires ultra-cold freezers set at minus 70 degrees Celsius (-94 degrees F). On February 19, however, Pfizer and BioNTech said that their vaccine can remain stable for two weeks at temperatures between minus 25℃ and minus 15℃ (-13℉ to 5℉), a common range in pharmaceutical freezers and refrigerators. The finding would allow for easier distribution of the vaccine in communities where ultra-cold storage requirements present a challenge. 

Efficacy: On September 20, Pfizer announced that a study of its clinical trials shows its vaccine is safe and highly effective in children ages five to 11. Researchers determined that two low doses administered three weeks apart elicit high levels of neutralizing antibodies among children, with side effects comparable to those seen in people ages 16 to 25. The 10-milligram doses of vaccine are a third of what has been approved among older age groups. The company later released an analysis of its clinical trials showing that the vaccine is 90.7 percent effective in preventing symptomatic disease among kids in this age group.

Pfizer also expects to release data soon on how well its vaccine works among children ages six months to five years, according to CEO Albert Bourla. In a public forum, he said the data could be available as early as the end of October.

On August 25, Pfizer announced new data showing that a third dose of its vaccine generates robust quantity of neutralizing antibodies that is more than three times higher than what was observed one month after the second dose.

A preprint study out of the United Kingdom shows that the Pfizer and AstraZeneca vaccines remain protective against the Delta variant but that their efficacy wanes over time. Among study participants, Pfizer’s vaccine waned more rapidly. Within four to five months after a second dose, the vaccine’s efficacy was on par with the AstraZeneca shot. The study emphasizes, however, the both vaccines still significantly reduce the risk of infection. 

On July 8, a study published in Nature demonstrated that people who have received both doses of the Pfizer or AstraZeneca vaccines remain fully protected against severe disease, hospitalization, and death from the Delta and Beta variants. However, a single dose of either vaccine was not as protective.

The findings corroborate an earlier study published in Nature showing that the Pfizer and Moderna vaccines elicit “robust and prolonged” immune responses. As the New York Times reported at the time, the findings suggested that people who are immunized with these vaccines may not need booster shots as protection may last for years so long as the virus doesn’t mutate to evade it.

On June 10, a study published in the journal Nature showed that two doses of the Pfizer vaccine protects against several virus variants, including the Delta and Eta variants. The news came a few days after the CDC announced that the Pfizer and Moderna vaccines reduce the risk of infection by 91 percent for fully vaccinated people. 

In April, the CDC released a study of the U.S. vaccine rollout showing that the Pfizer-BioNTech and Moderna vaccines are 90 percent effective in preventing symptomatic COVID-19 in real-world conditions. The study analyzed the efficacy of the two mRNA vaccines among nearly 4,000 health-care workers, first responders, and other frontline workers who were the first to receive the jab in the U.S. It also showed the vaccines are 80-percent effective after one dose. The findings confirmed earlier studies from the U.K. and Israel.

On December 10, the New England Journal of Medicine published the results of Pfizer’s phase three study, showing the vaccine was safe and 95-percent effective in protecting against COVID-19 in people 16 and older. Pfizer and BioNTech have also announced that a phase three trial shows that their vaccine is safe and 100 percent efficacious among children between the ages of 12 and 15, and that it elicited robust antibody responses. 

Safety: On June 23, the U.S. Food and Drug Administration said it plans to add a warning label to the Pfizer and Moderna vaccines about rare cases of heart inflammation in adolescents and young adults. The news comes after the CDC convened an emergency meeting of its advisory committee to discuss “rare but higher-than-expected” cases of myocarditis and pericarditis among young people who have received the vaccines. The committee acknowledged that these cases are likely linked to the vaccines but that the benefits of the shots outweigh the risks.

Severe allergic reactions following immunization with the Pfizer-BioNTech vaccine have been reported in many countries. White House advisor Anthony Fauci told CNBC in December that some adverse reactions are expected when a vaccine is distributed to a wider population. Regulators in the U.S. and U.K. have also released reports offering reassurances that severe reactions are rare.

Clinical trials status: On November 18, Pfizer and BioNTech announced the conclusion of their phase three trials. The trials launched in July, enrolling a diverse population in areas with significant SARS-CoV-2 transmission. Pfizer later expanded the trial to include 44,000 people across multiple countries. 

On February 18, Pfizer and BioNTech announced the launch of a phase two/three clinical trial to study the vaccine’s safety and efficacy among 4,000 pregnant women over the age of 18. The companies also launched a phase 1/2/3 study in children between the ages of six months and 11 years.

On June 8, Pfizer said that it would expand its clinical trials to a larger group of children under age 12. After a phase one study showed that the vaccine was safe and effective in a group of 144 children, the clinical trials enrolled up to 4,500 children at more than 90 sites in the U.S., Finland, Poland, and Spain. Pfizer tested a dose of 10 micrograms in children ages 5 to 11, and three micrograms for children from six months to five years old. 

On July 8, Pfizer and Biotech announced that they are developing an updated version of the vaccine that specifically targets the Delta variant.

Johnson & Johnson

Name: JNJ-78436735

Who: One of the world’s largest multinational corporations, based in New Jersey, specializing in healthcare and pharmaceutical products.

What: A single-dose vector vaccine. (Here’s how the Johnson & Johnson vaccine works.)

Approval status: Approved for use in the U.S., Bahrain, Canada, and the European Union.

On October 21 the CDC cleared the way for the U.S. to begin rolling out booster shots of Johnson & Johnson’s vaccine for all people ages 18 and older at least two months after a first dose. 

U.S. regulators also authorized mixing and matching vaccines—such as administering booster doses of the either Moderna or Pfizer vaccine to people who originally received the Johnson & Johnson vaccine. A preprint analysis of a National Institutes of Health study shows that a booster dose of the mRNA vaccines elicit a stronger immune response than another dose of the Johnson & Johnson shot. 

Distribution: On March 2, the U.S. announced that Johnson & Johnson has partnered with its competitor Merck to increase the supply of its COVID-19 vaccine. Merck will dedicate two facilities to producing the vaccine, which could double the amount of available doses. Biden said that the additional doses will allow the U.S. to vaccinate all adults by the end of May. 

On June 11, the New York Times reported that the FDA has told Johnson & Johnson to throw out 60 million doses made at its plant in Baltimore. The news came a day after CNN reported that the U.S. hasn’t sent any shipments of the vaccine since the first week of May due to a lack of supply caused by earlier issues at the plant. On June 10, Johnson & Johnson also announced that the FDA has approved an extension of the shelf life of its vaccine from three to four and a half months. 

Efficacy: In September 2021 Johnson & Johnson announced results of its studies of booster doses. When administered two months after the first jab, the booster is 100 percent effective against severe disease and causes antibody levels to rise four to six times higher than after the first shot. The second dose was also shown to be 75 percent effective against all symptomatic disease globally and 94 percent effective in the U.S. The company said that a booster shot administered six months after the first dose produced a 12-fold increase in antibody levels.

The company also said that real-world evidence shows that its single-dose vaccine remains effective against COVID-19. The press release cited a study published to a preprint server, which shows that the vaccine remains 79 percent effective in preventing COVID-19 and 81 percent effective in preventing hospitalizations. An earlier study conducted by Johnson & Johnson shows that its vaccine offers strong protection against Delta that lasts for at least eight months. 

However, on July 20, the New York Times reported on a preliminary study showing that Johnson & Johnson’s vaccine is less effective against the Delta and Lambda variants than it was against the original virus strain. The paper notes that the results were obtained in a lab experiment and may not reflect the vaccine’s real-world efficacy.

On February 24, an FDA analysis confirmed Johnson & Johnson’s earlier report that its vaccine is safe and effective in preventing COVID-19. The report found the vaccine is 72-percent effective in preventing COVID-19 based on U.S. trials, and 85-percent effective in preventing severe disease across all regions. It also shows that the vaccine was 64-percent effective in preventing disease in the company’s South African trials, which is higher than had previously been reported.

On June 9, a study published in the journal Nature showed that Johnson & Johnson’s vaccine is effective in protecting against virus variants, including the Beta and Gamma variants of concern. The study showed that the vaccine elicits neutralizing antibodies and a T-cell response among people who live in areas where the variants are widely circulating, including Brazil and South Africa. 

Safety: On July 13, U.S. regulators added a warning to Johnson & Johnson’s vaccine in response to rare reports linking the shot to Guillain-Barré Syndrome, a disorder in which the body’s immune system attacks the nerves. The FDA said there have been about a hundred preliminary reports of the syndrome among the 12.8 million people who have received the Johnson & Johnson vaccine. It added that the benefits of receiving the vaccine still outweigh the risks. 

CDC officials told the Washington Post that the cases have mostly been reported about two weeks after vaccination among men, many aged 50 or older, and that these cases will be discussed during an upcoming meeting of the CDC’s advisory committee. 

In the spring, the vaccine’s rollout was briefly halted in the U.S. and across Europe as regulators investigated reports of blood clotting among people who have received the shot. The FDA and CDC reviewed 15 cases of blood clots. The cases—which the agencies noted are “extremely rare”—occurred in women between the ages of 18 and 48 within six to 13 days after vaccination. The Europeans Medicines Agency also said that the cases it reviewed occurred in people under 60—mostly women—within three weeks of vaccination. 

On April 23, the U.S. FDA and CDC lifted the pause on Johnson & Johnson’s vaccine and said that immunizations can resume immediately. The agencies said that the risk of blood clots is “very low” and that the benefits of getting the vaccine outweigh the risks. It will add information about the increased risk of blood clots to the vaccine’s label. The decision came days after the European Medicines Agency said that blood clots should be listed as a “very rare” side effect of Johnson & Johnson’s COVID-19 vaccine. 

Clinical trials status: On September 23, 2020, Johnson & Johnson announced the launch of its phase three “ENSEMBLE” trial to evaluate the safety of the vaccine—and how well it works—among up to 60,000 adults from a variety of countries. The trial included “significant representation” from older populations and those with underlying conditions that make them more susceptible to COVID-19. 

On October 12, 2020, Johnson & Johnson announced that it paused phase three trials for an independent safety review due to an unexplained illness in a participant. The company didn’t provide any details, in part to protect the patient’s privacy, but said that illnesses and accidents are expected in large clinical studies. What’s more, study pauses are routine for clinical trials and aren’t typically reported. Later that month, the company announced it would resume trials, which were fully enrolled with 45,000 participants by December 17.

On November 15, 2020, Johnson & Johnson launched a second phase three trial to study the safety and efficacy of a two-dose regimen of its vaccine candidate in up to 30,000 volunteers worldwide. The study intends to assess whether a second dose of the vaccine will offer longer-lasting protection.

On April 2, Johnson & Johnson announced that it has begun vaccinating children age 12 to 17 as part of its phase 2a clinical trial. The company said it will initially test the vaccine in adolescents age 16 to 17 before expanding it to younger children.

Moderna Therapeutics

Name: mRNA-1273 

Who: A Massachusetts-based biotech company, in collaboration with the National Institutes of Health.

What: A nucleic-acid vaccine that requires two doses. 

Approval status: On December 18, the FDA granted emergency approval to Moderna’s COVID-19 vaccine, making it the second available in the United States. The vaccine has also been approved in the European Union, Canada, the U.K., Israel, and by the WHO.

On October 21 the CDC cleared the way for some people to get booster shots of the Moderna vaccine. The agency endorsed the FDA’s emergency use authorization of booster doses for all people ages 65 and older, as well as those ages 18 to 64 who are at risk of severe COVID-19 because of their underlying conditions. It also includes people ages 18 to 64 who are at high risk of exposure because of where they work or live, such as health-care workers or incarcerated people.

Moderna has applied for full FDA approval of its COVID-19 vaccine for use in people age 18 and older. The company also plans to file for emergency use authorization for teens ages 12 to 17. 

On October 5, Moderna announced that European Union regulators have authorized a third dose of its COVID-19 vaccine for “severely immunocompromised” people ages 12 and older. 

Distribution: The FDA has said that Moderna’s vaccine can now be kept at room temperature for up to a day. The vaccine can otherwise be safely stored on ice or in a normal refrigerator for 30 days. These changes are expected to help the company distribute its vaccine more quickly.

The company plans to deliver at least 500 million doses globally per year beginning in 2021, thanks in part to a deal it has struck with Swiss manufacturer Lonza that will allow it to manufacture up to a billion doses a year. 

Efficacy: A study of clinical trials among adolescents ages 12 to 17 shows that its vaccine is safe and 100 percent effective. The study also showed the vaccine is 93 percent effective among participants in this age group two weeks after the first dose.

Moderna has said that the phase two clinical trials of its booster dose showed that a third dose administered six months after the second “induce robust antibody responses” and increased protections against the variants of concern. It has also said that a study of the phase two clinical trials of its three booster candidates produced robust antibody responses against the virus, including the Gamma, Beta, and Delta variants of concern. 

However, there is some doubt about whether people who received the Moderna shot will need boosters. A study published in the journal Nature in June 2021 showed that the vaccine elicits “robust and prolonged” immune responses—indicating that protection may last for years so long as the virus doesn’t mutate to evade it.

On September 10, the CDC released a study of more than 32,000 real-world cases suggesting that Moderna’s vaccine is more effective at preventing hospitalizations than the Pfizer or Johnson & Johnson vaccines. The overall efficacy of Moderna’s vaccine was 95 percent, compared to 80 percent for Pfizer and 60 percent for Johnson & Johnson.  

The study backed up earlier studies suggesting that Moderna’s vaccine may provide stronger protection than Pfizer’s jab. A study published on August 30 found that Moderna’s vaccine produces significantly more neutralizing antibodies than Pfizer’s, which might be attributed to the higher dosage or the longer interval between the first and second doses. On August 8, a preliminary Mayo Clinic study of more than 50,000 patients showed that the efficacy of Moderna’s vaccine dropped from 86 percent in early 2021 to 76 percent in July, when the Delta variant was predominant. Meanwhile, the Pfizer vaccine’s efficacy dropped over the same time period from 76 percent to 42 percent. 

An earlier preprint analysis of Moderna’s vaccine also suggested that antibody levels can predict the vaccine’s efficacy against COVID-19. The study showed that people with breakthrough infections who had lower levels of antibodies in their blood were more likely to develop symptomatic infections than those with higher levels of antibodies. The study authors tell Nature that the data doesn’t suggest a threshold of antibodies that ensures protection but it does show a relationship between higher levels of antibodies and lower risk of infection.

On August 12, a study published in the journal Science showed that Moderna’s vaccine protects against COVID-19 for at least six months and is effective against the Delta variant. The findings confirm earlier studies and announcements made by the company that its vaccine remains 93 percent effective for at least six months after administration of the second dose.

On July 9, Nature reported on a study showing that two quarter-doses of Moderna’s vaccine generates long-lasting neutralizing antibodies and T cells. The results suggest that it might be possible to administer fractional doses to help stretch the world’s vaccine supply, particularly in low- and middle-income countries that are facing shortages.

On February 17, the New England Journal of Medicine published a preliminary report showing that Moderna’s vaccine remains effective in protecting against the virus variant found in the U.K. However, it may be less effective in protecting against the South African variant—although researchers noted that further study is needed. 

In December 2020, an FDA analysis of the phase three study of Moderna’s vaccine confirmed that it is 94.1-percent effective in preventing mild cases of COVID-19 and 100-percent effective at preventing severe cases after taking two doses.

Safety: On June 23, 2021, the U.S. Food and Drug Administration said it planned to add a warning label to the Pfizer and Moderna vaccines about rare cases of heart inflammation in adolescents and young adults. The news comes after the CDC convened an emergency meeting of its advisory committee to discuss “rare but higher-than-expected” cases of myocarditis and pericarditis among young people who have received the vaccines. The committee acknowledged that these cases are likely linked to the vaccines but that the benefits of the shots outweigh the risks.

Clinical trials status: Moderna announced on December 17, 2020, that it was launching clinical trials to evaluate the vaccine’s safety in children and people with cancer; it will also establish a “pregnancy registry” to track the vaccine’s safety in people who are pregnant. 

The company started the third phase of its clinical trials in July 2020. Preliminary findings from its phase one trials showed that healthy subjects—including elderly patients—produced coronavirus antibodies and a reaction from T cells, another part of the human immune response. Phase three tested the vaccine in 30,000 U.S. participants. 

On February 24, Moderna announced that it has shipped doses of a booster vaccine to the U.S. National Institutes of Health for clinical trials. The phase one trial will determine whether the booster can improve immunity against the South Africa variant. Moderna is also investigating using a third dose of its approved vaccine to protect against variants. 

AstraZeneca-University of Oxford

Name: ChAdOx1 nCoV-19 

Who: The U.K. university, in collaboration with the biopharmaceutical company AstraZeneca.

What: A viral vector vaccine that requires two doses.

Approval status: Approved for use in the United Kingdom, the European Union, Argentina, India, and other countries. It has also been authorized by the World Health Organization.

Efficacy: In August 2021 a preprint study out of the United Kingdom showed that the Pfizer and AstraZeneca vaccines remain protective against the Delta variant but that their efficacy wanes over time. Among study participants, Pfizer’s vaccine waned more rapidly. Within four to five months after a second dose, the vaccine’s efficacy was on par with the AstraZeneca shot. The study emphasizes, however, both vaccines still significantly reduce the risk of infection.

On July 8, a study published in Nature demonstrated that people who have received both doses of the AstraZeneca of Pfizer vaccines remain fully protected from the Delta and Beta variants. However, a single dose of either vaccine was not as protective.

On June 25, preliminary results from a British study showed that mixing doses of the AstraZeneca and Pfizer vaccines provides strong protection against COVID-19. Researchers told the New York Times that the protection is strong regardless of the order in which the vaccines are administered. The findings will be useful for those who are unable to get a second AstraZeneca vaccine due to production delays and safety concerns, although researchers say it’s still best to get two doses of the same vaccine for now.

On March 24, AstraZeneca released the primary analysis of its U.S. phase three clinical trials showing that its vaccine is 76 percent effective at preventing COVID-19, slightly lower than the 79 percent efficacy it had announced two days earlier based on a partial analysis of the data. It is also 85 percent effective in people 65 and older and 100 percent effective at preventing severe cases of the disease.

U.S. health officials had taken the unusual step of questioning the decision to release the interim results, describing them as “outdated and potentially misleading.” In a letter obtained by the Washington Post, an independent panel of experts at the National Institutes of Health that oversees U.S. clinical trials said that it had recommended the company release a later analysis instead, showing the vaccine may be 69 to 74 percent effective.

The companies also said that the vaccine’s efficacy increased to 82 percent when the second dose was taken after 12 weeks or longer, rather than the originally recommended four-week interval. The British government has recommended the longer gap in its rollout of the vaccine to prioritize getting the first shot to as many at-risk people as possible. 

On February 7, South Africa halted its use of the AstraZeneca-Oxford vaccine after preliminary laboratory studies showed it offered only minimal protection against the virus variant that is dominant in that country. The finding was later confirmed by a study published in the New England Journal of Medicine showing that the vaccine does not protect against mild to moderate cases of COVID-19 caused by the South African variant. Early data suggested that the vaccine will still effectively protect against the variant that is prevalent throughout the U.K.    

Safety: On June 9, a study published in the journal Nature Medicine found that people who have received the AstraZeneca vaccine have a slightly increased risk of a bleeding disorder. The analysis of 2.53 million people who received the vaccine found an incidence of 1.13 cases per 100,000 vaccines. Researchers said the benefits of getting the vaccine outweigh the risks. The study echoed an earlier safety review conducted by the European Medicines Agency.

In Canada, meanwhile, on June 29 regulatory officials advised people with a history of capillary leak syndrome against receiving the AstraZeneca vaccine. Health Canada is also updating the vaccine’s label to add the syndrome as a potential side effect.

Distribution: Project members say their candidate can be stored at temperatures seen in common refrigeration. Oxford and AstraZeneca expect to produce up to three billion doses of the vaccine in 2021.

On December 30, the U.K. announced changes to its vaccine delivery plan to prioritize delivering the first dose of either vaccine to as many at-risk people as possible, based on data provided to and released by health regulators. It did so by delaying administration of the second dose of the AstraZeneca-Oxford drug. A similar rule was issued for the Pfizer-BioNTech vaccine, but regulators didn’t provide data to back the new regimen. Overall, the U.K. still recommends that recipients receive two doses of either vaccine for maximum benefit. 

Clinical trials status: On December 11, AstraZeneca and Russia’s Gamaleya Institute announced plans to work together to study the possibility of combining Oxford’s vaccine with Gamaleya’s Sputnik V vaccine. Since both use the same adenovirus, researchers will investigate whether a combination of the two will improve efficacy. 

The AstraZeneca-Oxford vaccine’s phase three trial aimed to recruit up to 50,000 volunteers in Brazil, the U.K., the United States, and South Africa. On September 8, AstraZeneca paused the trials for a safety review due to an adverse reaction in one participant in the U.K., which the company described as a “routine action.” After an investigation by independent regulators, the trials resumed in the U.K., Brazil, South Africa, and India in September and resumed in the U.S. a month later.

Novavax

Name: NVX-CoV2373

Who: A biotechnology company based in Gaithersburg, Maryland.

What: A protein vaccine that involves a nanoparticle carrier to better aid delivery and uptake by cells. The vaccine is administered in two doses, 21 days apart. 

Approval status: Authorized for emergency use in Indonesia.

Novavax has not yet submitted its vaccine to the FDA for emergency use authorization, but it is planning to do so. Reuters reports that Novavax also said that it will file a separate application for booster shots once the emergency use authorization submission is processed; the company said its booster shot given six months after the two-dose regimen elicited a 4.6-fold increase in antibodies. The company has filed for authorization from regulators in India and the Philippines.

Efficacy and safety: On June 14, Novavax announced that its vaccine is safe and 90.4 percent effective in protecting against COVID-19—including the more contagious virus variants that are circulating. The vaccine is also 100 percent effective at preventing moderate and severe disease among 29,960 clinical trial participants age 18 and older in the U.S. and Mexico. 

On March 11, Novavax announced that a final analysis of its phase three clinical trials in the U.K. shows that its vaccine is 96.4-percent effective in preventing COVID-19. It also announced the findings of its phase 2b clinical trial in South Africa, which showed the vaccine was only 48.6-percent effective against the strains circulating there. Both trials showed the vaccine is 100-percent effective at preventing severe cases of the disease. 

On January 28, 2021, Novavax had announced preliminary results of its phase three trials in the U.K., which showed at the time that its vaccine is 89.3-percent effective in preventing COVID-19. On September 2, 2020, a study of the company’s phase one trial published in the New England Journal of Medicine found that the vaccine was safe and produced coronavirus antibodies at a higher level than is seen among those who have recovered from COVID-19. It also stimulated T cells, another arm of the human immune response.

Clinical trials status: On September 24, 2020, Novavax announced the launch of its phase three trial in the United Kingdom, which evaluated the vaccine in up to 10,000 people, both with and without underlying conditions. Up to 400 participants were also vaccinated against the seasonal flu as part of a sub-study to help determine whether it is safe to give patients both vaccines at the same time. On November 30, Novavax said it had completed enrollment in its phase three trial in the U.K.

On December 28, 2020, Novavax announced the launch of a phase three study in the U.S. and Mexico, which evaluated the safety and efficacy of its vaccine in up to 30,000 adults. 

Sinopharm

Name: None 

Who: China’s state-run pharmaceutical company, in collaboration with the Wuhan Institute of Biological Products.

What: Two inactivated SARS-CoV-2 vaccines. 

Approval status: China has approved one of the company’s vaccines for general use and another for limited use. One of the Sinopharm vaccines has also been approved by the World Health Organization as well as in Bahrain, the United Arab Emirates, and other countries.

Sinopharm filed for final regulatory approval from China in late November, two months after the New Yorker reported that hundreds of thousands of Chinese civilians have already been vaccinated under the government’s emergency-use approval. China began to innoculate medical workers and other high-risk groups with the Sinopharm trial vaccines in July, making it the first experimental vaccine available to civilians beyond clinical volunteers. 

Efficacy and safety: On July 19 preliminary results from a study conducted in Sri Lanka found that Sinopharm’s vaccine was less effective against the Delta variant than the original SARS-CoV-2 strain. As Reuters reported, the study showed that the vaccine elicited a 1.38-fold reduction in antibody levels against the variant.

On May 7, the World Health Organization estimated the Sinopharm vaccine’s efficacy to be 79 percent among all age groups, affirming the company’s earlier announcement of the results of its phase three study.

Preliminary findings from two randomized trials, published in the Journal of the American Medical Association, have shown the vaccine can trigger an antibody response with no serious adverse effects. The study did not measure T cell-mediated immune responses. These results are significant, though, as they are the first published data from human clinical trials for a COVID-19 vaccine that uses a whole, inactivated virus.

Clinical trials status: Sinopharm launched its first phase three trial in July 2020 among 15,000 volunteers—aged 18 to 60, with no serious underlying conditions—in the UAE. The company selected the UAE because it has a diverse population made up of approximately 200 nationalities, making it an ideal testing ground. Sinopharm also conducted phase three trials in locations such as Peru and Bahrain.

Sinovac

Name: CoronaVac 

Who: A Chinese biopharmaceutical company, in collaboration with Brazilian research center Butantan.

What: An inactivated vaccine. 

Approval status: Approved for limited use by the WHO as well as in China, Indonesia, Brazil, and other countries.

Efficacy and safety: On July 15 Reuters reported that the leaders of a Chilean study have recommended administering a third dose of Sinovac’s vaccine as its efficacy has waned in the face of the Delta variant. The vaccine’s level of protection is lower than others—late-stage trials found that it is 51 percent effective in preventing COVID-19. Still, Nature reports that it is 100 percent effective at preventing severe disease and therefore is key to helping curb the pandemic. 

On April 7, a preliminary study of CoronaVac’s vaccine rollout in Brazil showed that the vaccine is about 50 percent effective in protecting against COVID-19 in a region where the highly transmissible P.1 variant is circulating. 

Clinical trials status: CoronaVac entered phase three trials in July, with plans to recruit nearly 9,000 healthcare professionals in Brazil, in addition to phase three trials in Indonesia. A planned trial in Bangladesh was delayed, after Bangladesh refused in October to co-finance a late-stage trial. 

Center for Genetic Engineering and Biotechnology

Name: Abdala

Who: A government-run research institute in Cuba.

What: A protein subunit vaccine that’s administered in three doses.

Approval status: Approved for emergency use in Cuba and Vietnam. Prior to granting emergency use authorization, Cuba had already begun administering the vaccine among health workers as part of an “intervention study.”

Efficacy and safety: On June 22 Cuba announced that the Abdala vaccine is 92.28 percent effective against COVID-19. 

Clinical trials: In March Cuba launched phase three clinical trials for the Abdala vaccine among 48,000 volunteers.

Finlay Institute for Vaccines

Name: Soberana-02

Who: A government-run research institute in Cuba.

What: A conjugate vaccine that uses part of the virus spike protein.

Approval status: Authorized for emergency use in Cuba and Iran.

Efficacy: On June 22 the New York Times reported that the Soberana-02 vaccine was 62 percent effective at preventing COVID-19 after two of its three required doses. 

Clinical trials: On March 4, Cuba became the first country in Latin America to announce the launch of a phase three clinical trial for one of its COVID-19 vaccines, the Miami Herald reported. The Cuban government said the phase three trial would be conducted in Havana among 44,000 volunteers.

CureVac

Name: CVnCoV

Who: A German biopharmaceutical company in partnership with Bayer, a German multinational pharmaceutical company.

What: An mRNA vaccine that’s administered in two doses taken 28 days apart.

Approval status: Not approved for use. On October 12, 2021, CureVac announced that it was withdrawing its COVID-19 vaccine candidate months after it reported disappointing results from a study of its clinical trials showing its vaccine was only 47 percent effective in preventing COVID-19, falling short of the company’s own criteria for success. CureVac attributed its results to the virus variants that were circulating at the time. It sequenced 124 cases of COVID-19 among clinical trial participants and found only one case was caused by the original SARS-CoV-2 virus and more than half were caused by variants of concern.

Efficacy and safety: On January 11, CureVac announced that preliminary results show its vaccine prompted robust antibody and T-cell responses in rhesus macaques. 

Clinical trials status: On December 14, 2020, CureVac announced it had begun enrolling participants in a phase 2b/3 study to assess its vaccine’s safety and efficacy in more than 35,000 participants in Europe and Latin America. One week later, the company launched a separate phase three trial in healthcare workers in Mainz, Germany.

Sanofi and GSK

Name: None

Who: A global biopharmaceutical company in partnership with a global healthcare company.

What: An adjuvant-supported recombinant-protein vaccine.

Approval status: Not approved for use.

Efficacy and safety: On May 17, the companies announced that a study of their phase two clinical trials shows the vaccine generated a high level of neutralizing antibodies with no safety concerns.

Clinical trials: On May 27, 2021, Sanofi and GSK announced that they had started to enroll participants in a phase three clinical study to test the safety and efficacy of their vaccine in 35,000 volunteers ages 18 and older in the U.S., Asia, Africa, and Latin America. The study’s broad geographic range was intended to allow the companies to evaluate the vaccine’s efficacy against variants of concern.

Biological E. Limited

Name: None

Who: An Indian vaccine and pharmaceutical company in partnership with the Baylor College of Medicine.

What: A protein-based subunit vaccine that requires two doses administered 28 days apart.

Latest news: On April 26, the companies announced that they received approval to launch a phase three clinical trial of their vaccine candidate. The trial will evaluate the efficacy and safety of the vaccine among more than 1,200 volunteers ages 18 to 80 at 15 sites across India.

Approval status: Not approved for use.

Distribution: If the vaccine is approved for use, it will be distributed through the COVAX Facility, a global effort to ensure the equitable distribution of COVID-19 vaccines.

Valneva SE

Name: VLA2001

Who: A vaccine developer based in France.

What: An inactivated virus, adjuvant-supported vaccine, with two doses administered three weeks apart.

Approval status: Not approved for use. The company has initiatied rolling submission for approval with U.K. and European regulators.

Safety and efficacy: On October 18 Valneva announced that its vaccine elicited higher antibody levels than the AstraZeneca vaccine and “significantly fewer” adverse events among participants age 30 and older.

On April 6, Valneva announced that a study of its phase 1 and 2 clinical trials show that its vaccine prompted a strong immune response with no safety concerns.

Clinical trials: On April 21 Valneva announced the launch of phase three clinical trials to study the safety and efficacy of its COVID-19 vaccine compared to that of AstraZeneca’s conditionally approved vaccine. Approximately 4,000 volunteers were expected to receive two doses of either vaccine to determine the immune response of each. Valneva says it hopes to file for regulatory approval in the fall of 2021.

Shenzhen Kangtai Biological Products

Name: None.

Who: A China-based pharmaceuticals company

What: An inactivated vaccine that requires two doses administered 28 days apart.

Approval status: Authorized for emergency use in China. The country approved the Kangtai shot for emergency use in May 2021, just weeks after the vaccine launched its phase three clinical trials.

Clinical trials: Kangtai’s phase three clinical trials are underway, testing the vaccine’s safety and efficacy among 28,000 adults age 18 and older.

Medicago

Name: CoVLP

Who: A Canadian biotechnology company, in partnership with British multinational pharmaceutical company GlaxoSmithKline.

What: A plant-derived recombinant vaccine with an adjuvant that requires two doses administered 21 days apart.

Efficacy and safety: In May 2021 Medicago reported that interim data from its phase two clinical trial showed that its COVID-19 vaccine elicited high levels of neutralizing antibodies with no severe adverse reactions.

Clinical trials: On March 16, Medicago and GlaxoSmithKline announced that their vaccine had entered phase three clinical trials to study its safety and efficacy in up to 30,000 volunteers in 10 countries, including Canada and the U.S.

Bharat Biotech

Name: COVAXIN

Who: An Indian biotechnology company, in collaboration with the Indian Council of Medical Research and the National Institute of Virology.

What: An inactivated vaccine, which requires two doses that are administered 28 days apart. 

Approval status: Authorized for emergency use in India, Mexico, the Philippines, and other countries. The WHO has also listed the vaccine for emergency use.

Efficacy and safety: In November 2021 the WHO said that its analysis of COVAXIN shows the vaccine is 78 percent effective against COVID-19 and “is extremely suitable for low-and-middle-income countries due to easy storage requirements.” 

On March 3 Bharat Biotech announced that an interim analysis of its phase three trial showed its vaccine is 81-percent effective in protecting against COVID-19 after the second dose. A separate preliminary study also indicated that the vaccine produces antibodies that can neutralize the virus variant that originated in the U.K. 

On January 21, The Lancet published interim findings from COVAXIN’s phase one study that showed the vaccine elicited an immune response in participants. The study identified only one serious adverse event, and it was unrelated to the vaccine.

Clinical trials status: On November 16, Bharat Biotech announced it had begun phase three trials involving 26,000 participants at more than 25 centers across India.

The Gamaleya National Center of Epidemiology and Microbiology

Name: Sputnik V

Who: A Russian research institution, in partnership with the state-run Russian Direct Investment Fund.

What: A viral vector vaccine that uses two strains of adenovirus and requires a second injection after 21 days to boost the immune response. 

Approval status: In August, Russia cleared the Sputnik V vaccine for widespread use and claimed it as the first registered COVID-19 vaccine on the market—before the vaccine’s phase three trials had begun and despite the lack of published evidence at the time. It has since been approved in Belarus, Argentina, Venezuela, and other countries.  

On March 4 the European Union announced that it would begin a rolling review of the Sputnik V vaccine. The announcement came after a handful of European countries said they would consider approving the vaccine without E.U. approval. Hungary has already authorized the vaccine. But on October 21 Reuters reported that European regulators are unlikely to make a final decision until early 2022.

Efficacy and safety: On February 2, the medical journal The Lancet published the results of a phase three trial in Moscow that found the Sputnik V vaccine is safe and 91.6-percent effective in preventing COVID-19. The study, which involved more than 22,000 participants, also showed the vaccine is 100-percent effective in preventing moderate or severe cases of the disease, as no such cases were confirmed at least 21 days after receiving the first dose. 

Distribution: Global demand for Sputnik V soared in the weeks after the vaccine’s efficacy data was published. The vaccine makers reached deals with more than 40 countries in Latin America, Eastern Europe, Asia, and Africa. On February 19, the African Union announced that Russia has offered them 300 million doses of the Sputnik V vaccine. 

Clinical trials status: On December 11, the Gamaleya Institute and biopharmaceutical company AstraZeneca announced they will work together to study the possibility of combining Sputnik V with the candidate that AstraZeneca has developed with the University of Oxford. Since both candidates use the same adenovirus, researchers will investigate whether combining them will improve efficacy of the AstraZeneca vaccine, which is 70.4-percent effective in preventing COVID-19. 

Chumakov Center

Name: CoviVac

Who: A Russian research center.

What: An inactivated vaccine given in two doses, 14 days apart.

Approval status: On February 20, Russia approved the CoviVac vaccine for use even though late-stage clinical trials to test its safety and efficacy have not yet begun. Reuters reports that early-stage trials with 200 participants showed the vaccine has no side effects.

Distribution: The Chumakov Center plans to produce half a million doses per month.

Murdoch Children’s Research Institute

Name: Bacillus Calmette-Guerin BRACE trial 

Who: The largest child health research institute in Australia, in collaboration with the University of Melbourne.

What: For nearly a hundred years, the Bacillus Calmette-Guerin (BCG) vaccine has been used to prevent tuberculosis by exposing patients to a small dose of live bacteria. Evidence has emerged over the years that this vaccine may boost the immune system and help the body fight off other diseases as well. 

Efficacy and safety: On November 10, 2020, a U.S. study published in the Journal of Clinical Investigation found that among 6,201 healthcare workers in Los Angeles, those who had previously received the BCG vaccine reported symptoms of COVID-19 less often than those who hadn’t, a finding that study authors say strengthens the case for further research. In October of that year, the U.K. launched a study of the BCG vaccine that is part of the Australian-led trials. The study is seeking to recruit a thousand frontline health-care workers to test the vaccine’s effectiveness against COVID-19. 

Clinical trials status: In Apri 2020, researchers from the Murdoch Children’s Research Institute began a series of randomized controlled trials that will test whether BCG might work on the coronavirus as well. They aim to recruit 10,000 healthcare workers in the study. In an April 2020 scientific brief, the World Health Organization found that there is no current evidence that the BCG vaccine protects people against infection with the coronavirus. 

Approval status: Not approved for use.

CanSino Biologics

Name: Ad5-nCoV

Who: A Chinese biopharmaceutical company.

What: A viral vector vaccine. 

Approval status: On June 25, 2020, CanSino became the first company to receive limited approval to use its vaccine in people even though it was still in the second phase of its clinical trials. At the time, the Chinese government pproved the vaccine for military use only, for a period of one year. Since then, the vaccine has been approved in China, Argentina, Hungary, and other countries.

Efficacy and safety: Preliminary results from phase two trials, published in The Lancet, have shown that the vaccine produces “significant immune responses in the majority of recipients after a single immunisation.” There were no serious adverse reactions documented.

Clinical trials status: On December 21, CanSino announced that it has recruited more than 20,000 participants for its phase three trials in Pakistan, Russia, Mexico, and Chile. On August 15, Russian biopharmaceutical company Petrovax announced it had launched the first phase three clinical trial of Ad5-nCoV.

Vector Institute

Name: EpiVacCorona

Who: A Russian biotechnology institute.

What: A protein vaccine, namely it uses small fragments of viral antigens called peptides to produce an immune response.

Approval status: On October 14, 2020, Russia granted regulatory approval to EpiVacCorona even though the vaccine candidate had not published any results and had not entered phase three of its clinical trials. It is the second vaccine candidate that Russia approved for use despite a lack of published evidence about its safety and efficacy. It has since been approved for use in Turkmenistan and authorized for emergency use in Belarus.

Efficacy and safety: On January 13, 2021, Russian state news agency TASS reported that of the more than 2,000 volunteers who had received both doses of EpiVacCorona’s two-dose regimen, none reported adverse reactions from the vaccine. 

Clinical trials: In November 2020 Russia launched mass trials of its EpiVacCorona vaccine; the trials will inoculate 150 people over the age of 60 and 3,000 volunteers over the age of 18.

Zydus Cadila

Name: ZyCoV-D

Who: An Indian pharmaceutical company.

What: A DNA-based vaccine that is delivered by a skin patch.

Approval status: Approved for emergency use in India.

Safety and efficacy: In December 2020 Zydus Cadila said that a combined phase one/two study of its vaccine showed it was safe and prompted an immunogenic response, but the company did not share any data.

Clinical trials: On January 3, 2021, Zydus Cadila announced it had received approval from Indian regulators to launch a phase three trial testing the safety and efficacy of its vaccine in about 30,000 volunteers.

Anhui Zhifei

Name: ZF2001

Who: A Chinese biopharmaceutical company, in partnership with the Institute of Microbiology at the Chinese Academy of Sciences.

What: A subunit vaccine that uses pieces of protein from a pathogen to trigger an immune response.

Approval status: Approved for use in China, Indonesia, and Uzbekistan.

Efficacy and safety: In August 2021 a study of the company’s phase one and two clinical trials published in The Lancet showed that the vaccine elicited neutralizing antibodies and that the most common adverse reactions were cough, fever, and headache.

Clinical trials: In November 2020 Chinese health officials announced the launch of phase three trials for the Anhui Zhifei vaccine. The trials—which aimed to recruit 29,000 volunteers aged 18 or older—were expected to be conducted in China, Indonesia, Pakistan, and Ecuador.

Research Institute for Biological Safety Problems

Name: QazCovid-in

Who: A research institute in Kazakhstan.

What: An inactivated vaccine.

Approval status: Granted temporary registration in Kazakhstan in January 2021 despite a lack of data from its phase three clinical trials.

Efficacy and safety: In August 2021 a study of the vaccines phase one and phase two clinical trials published in The Lancet found that the vaccine was safe with no severe adverse events recorded. The studies also found the vaccine elicited a neutralizing antibody response as well as a T-cell response.

Clinical trials status: In December 2020, the institute announced that the Kazakh Ministry of Health approved the launch of phase three trials to assess the vaccine’s safety and efficacy in 3,000 volunteers.

Institute of Medical Biology at the Chinese Academy of Medical Sciences

Name: Unknown

Who: A Chinese research institute.

What: An inactivated vaccine that requires two doses taken 14 days apart.

Approval status: Not approved for use.

Clinical trials: In December 2020, researchers launched phase three clinical trials to test the efficacy and safety of the vaccine in 34,020 participants in Malaysia and Brazil. 

Safety and efficacy: Preliminary results of the vaccine’s phase one trial showed that it prompted an immune response with no serious adverse incidents.

Editor's note: This story was originally published on July 31, 2020. It was regularly updated as developments occurred until November 2021.

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