The first coronavirus vaccine shots administered across the country have raised hopes for a breakthrough in the fight against COVID-19, but experts are now raising an even more hopeful possibility: that people might only need one shot instead of the current two-dose regimen.
The prospect would effectively double the number of vaccine doses available and allow more people to be vaccinated quickly. But the idea has set off a debate, with experts saying there isn’t enough evidence yet to justify a single dose and people should plan to get two doses.
The push in favor of exploring the idea of a single-dose vaccine crystallized with a recent New York Times op-ed from Michael Mina, an immunologist at the Harvard T.H. Chan School of Public Health, and Zeynep Tufecki, a sociologist who has written extensively on the pandemic.
They called for immediately starting a new clinical trial to study whether one dose of the vaccine is sufficient. They cited data from the trials already conducted for the Pfizer and Moderna vaccines that showed protection began after the first dose, with as much as around 90 percent efficacy, compared to around 95 percent efficacy after two doses.
There are questions about how long protection will last without the second, booster dose, but Mina and Tufecki wrote the possibility of needing just one dose should be immediately studied.
“If that’s shown to be the case, this would be a game changer, allowing us to vaccinate up to twice the number of people and greatly alleviating the suffering not just in the United States, but also in countries where vaccine shortages may take years to resolve,” they wrote.
Part of the question is how aggressive to be pushing forward with a single dose that might be somewhat less effective than two doses, but would spread protection to twice as many people at a time when an average of around 2,500 Americans are dying from the virus every day and vaccines are not on track to be widely available for months.
“What can we do right now so that in a month we have not had 60,000 people dead?” said Christopher Gill, a professor of global health at the Boston University School of Public Health. He said there should at least be a debate about vaccinating twice as many people with a single dose immediately, without waiting for a new trial.
“If you wait, you may be dead,” he said.
Scott Gottlieb, a former Food and Drug Administration (FDA) commissioner, questioned the administration’s strategy of holding back half of the doses to make sure there is enough for everyone to get their second dose, given that in the worst-case scenario, a single dose is still at least partially as good.
The administration is holding back 2.9 million doses to serve as the second dose for the 2.9 million people being vaccinated in the first week rather than deploying all the doses at once, said Assistant Secretary of Health and Human Services Brett Giroir.
“We know that the first dose is partially protective, that data is out now, so you want to try to push out as many doses as possible to give as many people as possible some benefit,” Gottlieb, who is now on the board of Pfizer, said on CNBC earlier this month.
Other experts, including those at Operation Warp Speed and the FDA, are pushing back on those pointing to one dose, noting that months of careful study was conducted on the two-dose regimen.
“The second dose is a full part of the label if the vaccines are approved,” Moncef Slaoui, chief science adviser for Operation Warp Speed, said at a press briefing. “It consolidates the immunity into the patients against COVID-19, and that’s the data that shows long-lasting, at least over a few months, immunity. And I expect it to be very long-lasting. So people should not take the vaccine as a one-dose vaccine.”
Still, he left the door open to further study. “One could ask the question, why not run efficacy trials with a one-dose vaccine of the Moderna vaccine or the Pfizer vaccine?” he added. “That would be a valid question. Of course, timing would be a big challenge.”
Peter Marks, the FDA official overseeing vaccine review, noted at a separate press conference that the trials and reviews have been based on two doses.
“We spent so much time carefully reviewing the data and basing our decisions on science, that it seems pretty foolhardy to just conjecture that one dose might be OK, without knowing,” he said.
Mina, the Harvard professor, says the U.S. should conduct a new trial so it can know for sure, which he said would take two to three months.
“Even if it’s slightly inferior, from a public health perspective it might be superior,” he said of one dose, meaning that a slightly less effective vaccine spread over twice as many people would help reduce the overall spread of the virus faster.
Moderna said it has no plans for a new trial, though.
“We only studied a two dose regimen and believe it is highly efficacious across age groups with an expectation of durability,” a Moderna spokesperson said. “We currently do not plan to study a one dose regimen.”
In the meantime, Eric Topol, a professor of molecular medicine at Scripps Research, said it is important to communicate to people that they need to get two doses until more is known.
“The points for studying this are good but the public message to many for skipping the 2nd dose is troubling when we don’t really know what protection that provides,” he tweeted.
There is also another vaccine in the pipeline, from Johnson & Johnson, that could have results from its phase three trial early next year. The vaccine uses only a single dose.