What About Just One Dose of the Pfizer Vaccine?

Experts are calling for more research into a one-dose vaccine regimen

Credit: Heather Hazzan/SELF

The Covid-19 vaccine developed by Pfizer and BioNTech is likely going to be approved for emergency use in the United States very soon. When that happens, Americans can begin to be vaccinated.

One interesting finding that’s emerged during the review of Pfizer’s Covid-19 vaccine data is that the effectiveness of the vaccine appears to be pretty strong 14 days after the first dose. The vaccine requires two doses taken three weeks apart for full effectiveness. This is similar to other vaccines, like ones for HPV and hepatitis B, which require a multidose regimen for full protection.

But given how difficult it is to get people to take multiple doses of a vaccine — research on multidose vaccines like the hepatitis B immunization suggests that less than 50% of people return for their next dose — and given that the effectiveness after one dose seems pretty notable, some experts are wondering why Pfizer isn’t prioritizing a study on the long-term effectiveness of a single dose of its vaccine.

“At a minimum, there should be an immediate single-dose trial launched, like yesterday,” sociologist Zeynep Tufekci shares in her Twitter thread. “We sadly have a raging epidemic and will get results quickly but I think not giving this real thought now — and an explanation to the public — would be a grave mistake, given the stakes.”

The other argument for a single dose is that there are a limited number of vaccines available, and vaccination could take many months; a one-dose regimen would double the number of people who could be inoculated immediately. While two doses are obviously ideal, when looking at the overall context, is there a case for more people getting one dose versus fewer people getting two?

As you can imagine, expert opinions are split on the question, but there seems to be some agreement that more research inquiry into a one-dose strategy might be worthwhile.

Michael Mina, MD, PhD, an assistant professor in the department of epidemiology and the department of immunology and infectious diseases at Harvard, expressed his support for Tufekci’s view, sharing on Twitter that “One dose = 2x people vaccinated. The math is plain & simple.” He added that it’s clear the two doses are very important but that in an emergency scenario, if 80% of the two-dose effectiveness holds with a single dose of the vaccine, then vaccinating twice as many people is “the smart ethical approach.”

Other experts argue this line of thinking is counterproductive, saying that a lower dose of the vaccine is unlikely to provide as strong or as long of protection against Covid-19. “It will be an absolute disaster if a large number of people only take one dose of the vaccine,” shared Carlos del Rio, MD, a distinguished professor of medicine and executive associate dean for Emory at Grady. “It is very likely that protective immunity will wane rapidly in individuals who only take the first shot and efficacy will be nowhere near the 95% reported after the two-dose regimen.”

Natalie Dean, PhD, an assistant professor of biostatistics at the University of Florida, agreed that there’s too much uncertainty in the efficacy of a single dose regimen, adding that “the optics of changing the plan now, for a regimen that hasn’t been tested directly, are not great.” Though she did share support for follow-up studies.

Whether Pfizer and BioNTech will indeed start a study to look more closely at the long-term effect of a single dose remains to be seen. In the meantime, the priority will likely continue to be fully vaccinating the people most at risk.

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A blog from Medium for Covid-19 news, advice, and commentary.

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Alexandra Sifferlin

Alexandra Sifferlin

Health and science journalist. Former editor of Medium’s Covid-19 Blog and deputy editor at Elemental. TIME Magazine writer before that

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