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FDA Recommends Against Half-Doses and Other Vaccine Shortcuts

Untested shortcuts would cause confusion and be counterproductive, experts say

A researcher holds a COVID-19 mRNA vaccine

SOPA Images/Getty Images

En español | The Food and Drug Administration (FDA) Monday said calls to change the way two new COVID-19 vaccines are being administered in the U.S. are “premature and not rooted solidly in the available evidence.”

The FDA announced that it had been following discussions of administering half doses of the vaccine in two shots, or administering only one shot without the follow-up 21 or 28 days later, in order to extend its reach, but said in a statement: “Without appropriate data supporting such changes in vaccine administration, we run a significant risk of placing public health at risk, undermining the historic vaccination efforts to protect the population from COVID-19.”


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The rollout of the two vaccines that have received emergency use authorization in the U.S. (from Moderna and Pfizer-BioNTech) is slower than expected. While the federal government had promised that 20 million Americans would be vaccinated by the end of December, about 4.6 million had received their shot by Jan. 4. And they will need to receive a second vaccination soon (if they haven't had it already). The two vaccines were shown to be 95 percent effective in preventing COVID-19 in trials, based on a two-dose regimen: Pfizer-BioNTech vaccinations are meant to be given 21 days apart, Moderna's 28 days apart.

In response to the slow distribution of the vaccines, the rising COVID-19-related death toll in the U.S. (more than 350,000 as of Jan. 4) and the potential spread of an apparently more infectious form of the virus now prevalent in Britain, health officials have been considering certain shortcuts. Moncef Slaoui, Operation Warp Speed's chief scientific advisor, said in an interview on Sunday on CBS’ Face the Nation that experts were considering giving half of the recommended 100 microgram dose of the Moderna COVID-19 vaccine to people between the ages of 18 and 55. Studies have shown that that amount (in two doses) produces an identical immune response in that age group, Slaoui noted. Its efficacy for older people hasn't been studied.


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Others have also suggested administering only one shot, without the follow-up 21 or 28 days later (or with a far longer delay before the second dose, as is planned in Britain). In a Washington Post op-ed piece on Sunday, Robert M. Wachter, chair of the department of medicine at the University of California at San Francisco, and Ashish K. Jha, dean of the Brown University School of Public Health, asserted that “we should give people a single vaccination now and defer their second shot until more doses of vaccine become available … to vaccinate as many people as quickly as possible to save the most lives."

'Not supported by adequate scientific evidence'

But the FDA noted that such changes “are not supported by adequate scientific evidence” and “may ultimately be counterproductive to public health."

Barry Bloom, professor of public health in the department of immunology and infectious diseases at the Harvard T.H. Chan School of Public Health, agrees wholeheartedly with the FDA's caution: “What is the point of doing careful 50,000 person randomized controlled trials … only to say, ‘Forget about it, we're going to give one shot and we'll go find you at some later time. You'll have enough immunity maybe to get through.'”

Meanwhile, Bloom notes, the current problem isn't the number of shots available so much as the effective dissemination of them: Some 17 million doses have been shipped to U.S. states and territories, which have faced logistical challenges that have led to delays in administering the vaccines. “We do not have the infrastructure in most states to be able to handle the existing doses of vaccines that have been distributed,” says Bloom. “We're in no better position to handle twice that."

But even more important, perhaps, he adds, is maintaining the public's trust. “Anything that risks people not taking it, and being distrustful of the government or the vaccines or the process, is going to really hurt getting us to a level where we can go back to close to normal existence."

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