But Dr. Chris Gill, an infectious disease specialist at Boston University, points out that a single injection of Pfizer's vaccine may be even more effective than this estimate suggests. Looking at data from a smaller window between the time the first injection should have started working and before the second injection kicked in, Gill says the Pfizer-BioNTech vaccine may have an efficacy rate as high as 80 or 90% with just a single dose.
Moderna actually collected data from people who only received one dose of its vaccine, Gill says. Some 2,000 participants in Moderna’s phase three clinical trial received just a single injection of either a placebo or the vaccine. In that population, the efficacy of the single vaccine dose was roughly 80 to 90%.
“[Moderna] was not shy about showing that a single dose was so effective, and they do the math right," Gill says. “After 14 days, the [single dose] vaccine is remarkably effective.” //
Dr. Benjamin Linas, an epidemiologist also at Boston University, is still mulling over the question. There’s still a lot of information that is yet to be revealed, he says. For example, is it less effective to receive the second dose of the vaccine a few months later than recommended schedule?
“Probably not, but no one knows,” Linas says.
And nobody knows how long the protection from a single dose will last. Of course, nobody knows how long the protection from two doses of the vaccines will last, either. Beyond the roughly two-month period of the clinical trials, those studies haven't been done yet.
There is another concern throwing its shadow over the proposal to vaccinate more people now with a single dose: How to convince millions of people to show up for a second dose at an unspecified point in the future. It's hard enough to get people to arrive at pre-scheduled appointments for a second shot a month later, Linas says, let alone an unknown date based on an unknown supply of vaccines.
“If we gave all the vaccine now and back fill the second doses later, do we really have the logistical support to do that without entering chaos?” Linas says. “It makes me a little nervous.”
