Even as tens of millions of inoculated Americans breathe a collective sigh of relief after receiving either the one or two-dose COVID-19 vaccine, some wonder whether one round of shots is enough, or if they’ll need another—and another.
Scientists don’t yet know how long protection from the current cohort of coronavirus vaccines will last. Since the discovery of the original strain in late 2019, the virus has continued to mutate, yielding variants—similar-but-distinctive versions of the virus with the potential to be more infectious, deadly, and escape the antibody safeguards provided by the existing COVID-19 vaccines. To stay ahead of virus evolution, some vaccine creators are racing to design new shots to beat back variants while working to determine how long immunity lasts from current doses.
And the new “normal,” some experts say, could mean routine inoculation, or boosters, against COVID-19.
What’s a booster, anyway?
A booster shot is “a repeat dose of a vaccine that you’ve already received to literally boost your immunity,” says Susan R. Bailey, an allergist and clinical immunologist and president of the American Medical Association. The immune system creates virus-fighting memory from repeat exposure. It’s common that a second or third encounter with an antigen, a molecule that prompts antibody production, creates a “greater and more long lasting” immune response, Bailey says.
The shingles vaccine, for example, which is recommended for all healthy adults older than 50, requires a first shot and a booster two to six months later to ensure it is 90 percent effective at preventing the infection and its side effects.
The Pfizer-BioNTech and Moderna COVID-19 vaccines, which are mRNA vaccines, include an initial dose and a second shot three or four weeks later, respectively. Currently, the third COVID-19 vaccine authorized for emergency use in the United States, made by Johnson & Johnson, is given in a single dose, but the company is testing the efficacy of a second booster shot, too. (The U.S. has temporarily paused its distribution of Johnson & Johnson’s current dose, however, as it investigates reports of rare but severe blood clots.) In February, Pfizer-BioNTech launched a study of a third dose of its now two-dose regimen. And yesterday, Pfizer CEO Albert Bourla told CNBC that people would "likely" need a third shot, 12 months after the initial dose.
Each of these vaccines offer impressive efficacy against COVID-19 in their recommended doses. The question that remains, however, is how long that immunity will last—and whether additional shots will be needed in the near (or not-so-near) future to maintain that high level of protection.
The COVID-19 vaccines are brand-new, which means scientists don’t know yet how long they will remain effective without additional intervention. Researchers have monitored the effectiveness of the vaccines in inoculated people, and studies show that they remain highly effective for at least six months.
“Unfortunately, many people have misunderstood that to mean that it lasts only six months,” says Bailey, when, “all that information means is that we know that it lasts six months, and we expect it to last longer.” To know exactly how long protection endures, “we just have to wait and see.”
But, “it’s not obvious that every type of vaccination requires a booster,” says Amesh Adalja, an infectious disease physician and senior scholar at the Johns Hopkins University Center for Health Security. For example, the yellow fever vaccine offers lifelong protection after a single shot. And while the tetanus vaccine has long required a booster shot every 10 years to maintain its effectiveness, researchers have recently questioned whether additional doses are necessary.
What’s more, a vaccine booster is different from what some scientists are testing now: new shots targeted at specific variants.
There are at least five known "variants of concern" of the original SARS-CoV-2, the virus that causes COVID-19; B.1.1.7, which was first identified in the United Kingdom; B.1.351, first discovered in South Africa; P.1, which arose in Brazil; and both B.1.427 and B.1.429, which were first seen in California. Moderna has tweaked its vaccine and is currently testing whether it is efficacious against B.1.351—and a spokesperson for Pfizer told National Geographic that the company is discussing the potential for additional trials of vaccines that would target the variants currently circulating.
So far, the existing vaccines have proven to provide protection against these variants. “I don’t think we’re at that point where you pull a trigger, that you have to change something because of the variants,” Adalja says. But not every infectious disease expert agrees with that assessment.
The new normal
Daniel Lucey, an infectious-disease specialist with Georgetown University Medical Center, says that additional shots to boost immunity or target current or future variants “will most likely be a new reality” for some people. The virus will try to mutate “for its own survival benefit,” he says, and could escape the protection of current vaccines.
Lucey adds, “It’s a constant series of battles and multi-year war between SARS-CoV-2, its variants, and our vaccines, which are from 2019. We’re behind. The virus doesn't sleep, but we do.”
Matthew B. Frieman, an associate professor of microbiology and immunology at the University of Maryland School of Medicine who has worked with Novavax to develop its yet-to-be released COVID-19 vaccine, agrees. “It’s highly likely” that booster or brand-new shots will be “required in the future” to fight against SARS-CoV-2 variants, Frieman says. “How frequently we need them — and if they’re needed worldwide or in specific populations — is what we don’t know.”
Pfizer-BioNTech and Moderna’s mRNA vaccines are efficacious against the B.1.1.7 variant, which originated in the U.K. but is now the dominant strain in the U. S. But one initial study shows that B.1.351, the variant from South Africa, can break through at least the Pfizer-BioNTech vaccine. However, that study has not been peer reviewed—meaning that it has not yet been examined by a panel of experts—and included only a small sample size of people infected with the variant.
Earlier this month, Pfizer and BioNTech updated their COVID-19 vaccine’s efficacy, saying in an April 1 press release that it was 91 percent efficacious overall and “100 percent effective in preventing COVID-19 cases in South Africa, where the B.1.351 lineage is prevalent.”
Adalja says that if the vaccines dipped to 50 percent efficacy, then a booster or new shot might be needed. The U.S. Food & Drug Administration has said that it expects any COVID-19 vaccine to prevent disease or decrease severity in at least 50 percent of vaccinated people. When considering additional shots, “I think that is a good threshold to keep in mind,” Adalja says.
And if enough people get vaccinated not just in the U.S. but abroad, “you can block the spread of these variants,” says Frieman, which could impact the need for future shots. However, if boosters or new shots are needed, the same is true: people will need to take them en masse to be effective.
The ethical issues of boosters
Teneille Brown, a professor of law and adjunct professor of internal medicine at the University of Utah, says “asking or requiring people to get a booster might be a tougher sell for some,” because it “reflects an ongoing obligation and not a one-time thing.” Take the influenza vaccine, which is recommended for almost all people: only 45 percent of American adults got their annual shots during the 2017-2018 season; 48 percent got them for the 2019-2020 season.
While the U.S. government has not mandated COVID-19 vaccines, vaccine mandates are already taking shape: So-called “vaccine passports” may be required to board airplanes, for example, or to enter foreign countries. Some colleges are requiring on-campus students to be inoculated. And employers can require employees to get COVID-19 vaccines, though it’s unclear how many will.
If additional shots are needed, it’s conceivable that they could also be mandated in these same or similar ways. The burden of vaccine proof raises some ethics concerns, says Faith E. Fletcher, a public health ethicist in the Center for Medical Ethics and Health Policy at Baylor College of Medicine, and has the potential to exacerbate existing social and health inequities.
For example, essential workers and Black and Hispanic people have struggled more than their white counterparts to get initial vaccinations. Without finding ways to “make vaccines available and accessible to marginalized populations,” Fletcher says, “we’re going to see disparities down the line related to this issue,” including with any future COVID-19 shots, mandated or otherwise.
Brown and Fletcher agree that the cost of future doses should be covered. “There would need to be some requirement that the booster shots are covered by insurance, waiving copays, or they will not be equitably distributed,” Brown says, “and we will see gross inequities of who’s getting the booster and who’s not.” Even a $20 copay, she says, could keep people from getting a shot.
But for those who simply don’t want to follow work or private sector mandates for any future shots, “the law is not on their side,” Brown says. Existing laws permit mandates so long as exemptions are available for religious and medical reasons — for example, having an allergy.
Even so, Brown likens such mandates to driving a car.
“If you want to drive, you have to get a license, insurance, etc.,” Brown says. “It isn’t a one-time thing. The privilege of driving creates ongoing obligations to get your car registered, to get your emissions tested, and to continue to comply with changing traffic laws. You might disagree with these laws … but that doesn’t give you permission to ignore them at your choosing.”
Brown says that she is hopeful that any maintenance to keep COVID-19 at bay will become as routine as renewing a license or registration. “I actually think that the ongoing nature will help,” she says, because “resistance will fade with time and [as] vaccines become less politicized.”