In a report released on February 23, Osterholm and his colleagues calculate that temporarily prioritizing first doses for those over the age of 65 might save as many as 39,000 lives. “There is a narrow and rapidly closing window of opportunity to more effectively use vaccines and potentially prevent thousands of severe cases, hospitalizations, and deaths in the next weeks and months,” the authors write.
The UK adopted a similar strategy in December, and Quebec announced in January that it would stop holding back booster shots and try to vaccinate as many people as possible, delaying the second shot for up to 90 days.
But many public health experts, including senior advisors in the Biden administration, argue that there isn’t enough data to support a switch to a one-dose strategy. They worry that deferring the second dose will leave people vulnerable to infection, and potentially give rise to new variants that can evade the immune response. And there are logistics to consider. Switching strategies now would complicate the rollout, says Céline Gounder, an epidemiologist at the NYU Grossman School of Medicine and member of the Biden administration’s covid-19 Advisory Board. “You’re really having to break the current system, which is already very fragile,” she says. It also might hamper the public’s already tenuous trust in the vaccine.
“Given the information we have right now, we will stick with the scientifically documented efficacy and optimal response of a prime followed by a boost,” said Anthony Fauci, President Biden’s chief medical advisor, in a press briefing on February 19. Andy Slavitt, White House senior advisor on the COVID-19 response, agreed. “The recommendation from the FDA is two doses, just as it always has been,” he said.
The big protection question
The debate hinges on how much protection one dose really offers and how long that protection lasts.
In the large clinical trials, Moderna and Pfizer saw good efficacy even before the second shot. The first dose of the Pfizer vaccine provided 52% protection against symptomatic covid-19, and the Moderna shot achieved efficacy of 80%. But those figures included the days immediately after vaccination, when the immune system is still ramping up its response. When researchers looked at efficacy two weeks from the date of the shot, they found much higher numbers. One analysis suggests the Pfizer vaccine reached nearly 92% efficacy before the second shot. The first dose of the Moderna shot was 92% efficacious after two weeks.
And new research hints that one dose might offer some protection in a real-world setting too. In a new study in the New England Journal of Medicine, researchers examined medical records from nearly 600,000 vaccinated individuals in Israel and the same number of controls. The first dose of the Pfizer vaccine was 46% effective against SARS-CoV-2 infection between days 14 and 20. The shot did an even better job of preventing hospitalization and death: protection was 74% and 72%, respectively.