The U.S. may soon have a third vaccine. Here's how it works.

Johnson & Johnson’s COVID-19 vaccine is effective with just a single dose—but concerns swirl about lowered protection against one viral variant.

As the Biden administration works to accelerate the U.S. coronavirus vaccine rollout, it could soon have a new tool: A single-dose vaccine that can survive up to three months in an ordinary refrigerator.

Manufacturer Johnson & Johnson released data on January 29 showing that its single-dose version provided strong protection against COVID-19. On February 24, the U.S. Food and Drug Administration released an analysis of Johnson & Johnson’s vaccine confirming that it is safe and effective, and on February 26 a review committee within the agency recommended that the FDA authorize the shot for emergency use.

The news comes with two caveats: The candidate’s efficacy rate—72 percent in the United States—is lower than the 95 percent rates boasted by the two-dose versions from Pfizer-BioNTech and Moderna that are currently approved for use in the U.S.

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The Johnson & Johnson vaccine also provided less immunity among trial participants in South Africa, where a set of mutations threatens to accelerate the deadliness of the global pandemic. In that study, the efficacy rate was just 57 percent—although a more recent analysis has upped that number to 64 percent. The manufacturers of Pfizer-BioNTech and Moderna have reported similar concerns with their vaccines, and are studying different dosing and formulation strategies in the event new variants of the coronavirus outwit their vaccines.

If approved, though, experts say the Johnson & Johnson single-dose vaccine could streamline a national COVID-19 vaccination administration campaign that has been criticized as scattered and lethargic. Currently, the Pfizer-BioNTech and Moderna versions must be given in two doses several weeks apart.

“This could be a game-changer because it’s one dose,” says Bruce Y. Lee, professor of health policy and management at the City University of New York Graduate School of Public Health, who studies pharmaceutical supply chains. “It’s easier to administer. With two doses, you have to get people to come back for a second. It’s going to be easier to manufacture; you have to produce half as many doses.”

The absence of stringent temperature requirements for the Johnson & Johnson vaccine also means increased access across health systems and communities. Currently, the Pfizer-BioNTech vaccine must be stored at minus 94 degrees Fahrenheit and is good for five days in a refrigerator. Pfizer and BioNTech have submitted data to the FDA showing that their vaccine is stable at temperatures more commonly found in pharmaceutical freezers and refrigerators, but that evidence is still under review. Moderna’s version is shipped frozen and lasts up to 30 days in a refrigerator.

“Many clinics in lower income areas or rural neighborhoods might not have freezer space period, but they have refrigeration. It increases the range of places that can get the vaccines,” says Lee.

Proven vaccine technology

Another potential advantage of Johnson & Johnson’s candidate is that it’s made from a vaccine platform with a track record: the viral-vector approach, which the company used in its Ebola virus vaccine approved by the European Commission in July. By contrast, the Pfizer-BioNTech and Moderna vaccines are based on messenger RNA technology that was first authorized for use in humans in December.

Viral-vector technology uses an adenovirus, which causes the common cold. The strain of adenovirus used in the vaccine platform is engineered not to replicate, so that it doesn’t make the recipient sick. Rather, it serves as a vehicle to transport a gene from the SARS-CoV-2 virus that carries instructions to develop a part of the coronavirus—known as the spike protein—that allows it to invades cells. When introduced into the body, the altered adenovirus injects the gene into cell nuclei to produce the spike protein.

Yet the spike protein versions created by viral-vector vaccines are enough to fool the body into triggering an immune response to SARS-CoV-2 without causing an all-out infection. COVID-19 vaccines based on messenger RNA (mRNA), on the other hand, carry the instructions for generating spike proteins via RNA encoding for the spike protein coated with lipid nanoparticles.

“Conceptually it’s the same thing,” says Aliasger K. Salem, chair of pharmaceutical sciences at the University of Iowa. “The adenovirus is just like messenger RNA, but it uses a different vector.”

The significance of the Johnson & Johnson viral-vector vaccine, Salem adds, is that the company already has the knowledge of best practices and manufacturing infrastructure in place to quickly scale up production, if given the green light by the FDA.

It’s clear that Johnson & Johnson’s would gain competitive advantage by designing a single-dose regimen, but unknown whether its vaccine might provide better or longer protection if given with a booster shot. The company is currently attempting to answer that question by recruiting for a separate study that will give participants two doses spaced two months apart.

Such an additional dose could be a useful strategy for pharmaceutical companies to address new and worrisome variants of the virus that arise over time. For example, Moderna has said although it expects its current vaccine version to work against recently discovered variants from the U.K. and South Africa, its researchers planned to test a booster dose—a third shot in addition to the two-dose series—that would include specific spike proteins against emerging strains. One Moderna booster shot targeting the South African variant is already being studied in the U.S.

In late January, Pfizer-BioNTech announced new data showing that although its current vaccine formulation was slightly less effective against the South African variant, it still provided protection. Yet the companies were prepared to respond if it stopped providing immunity.

Viral-vector vaccines are also easily customizable, says Salem, whether as an emergency booster shot or a reconfigured single dose. “The industry has a long track record and experience with inserting new sequences into viral vectors so they can readily adapt to new variants,” he says.

The psychological difference

Whatever the FDA decides, several questions remain.

Will Johnson & Johnson’s “one-and-done” regimen convince more people to get a coronavirus vaccine? Or will the company’s successful track record with the viral-vector Ebola vaccine—in contrast to the new mRNA technology used by currently approved coronavirus vaccines—provide the necessary reassurance for people to sign up for the shot?

“I worry the word mRNA scares people. People are worried that it might mess with their genetics,” says Julie Swann, head of the department of industrial and systems engineering at North Carolina State University who studies health care systems. “We just don’t have the history with this particular kind of vaccine, even though we’ve been looking at this mRNA technology for a long time.”

Ultimately, convenience might matter more. “I don’t think most people dig into the details and actual mechanisms of vaccines,” says Austin Baldwin, an associate professor of psychology who studies vaccine decision-making at Southern Methodist University in Dallas.

Baldwin predicts the single-dose approach will result in increased vaccination rates. “The very fact that it’s a single dose means you’d expect compliance to be better. It reduces perceived barriers,” he says. “It’s easier to get one than two.”

Yet harder decisions still loom, as health officials have to weigh easier access with reduced protection, compared to the other two vaccines that are available. Despite reports of Johnson & Johnson’s lower efficacy rates, there were hopeful findings: The vaccine was 85 percent effective in preventing severe disease across the globe, and none of the vaccinated patients were admitted to the hospital. Plus, Johnson & Johnson has said it could produce 100 million doses by the end of June—providing a much-needed boost to the nation’s supply.

“One of my big questions is who should be given the Johnson & Johnson vaccine, if we know it’s less effective,” says Swann. “That’s a big issue. You wouldn’t want there to be inequities among different communities.”

If and when U.S. consumers are able to choose among available vaccine brands, they will also have to ask themselves which kind is best for them: one of the two-dose mRNA vaccines that give more than 90 percent protection?

“Or should I get the one dose and I won’t have to come back?” Swann says.

Editor's Note: This story has been updated with the latest FDA authorization status of the Johnson & Johnson vaccine. It originally published on January 29, 2021.

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