Americans are long used to making a single visit to a local clinic, getting a single jab, and thinking themselves done with flu for the season. Other than a few childhood vaccines, most vaccines are a one-and-done affair, and most people feel that they’re good to go once that bandage is applied to their arm. Of course, the truth is a little more complicated.
For the two vaccines that are likely to be first to obtain FDA clearance in the United States—the mRNA-based vaccines from Pfizer and Moderna—the way the vaccines are delivered is going to seem both a little strange and a little frustrating. In both cases, the vaccine is delivered in two doses. Patients go in for one jab, then get a second three to four weeks later. It’s not until about a week after that second dose that the full efficacy of the vaccine develops. So even someone who started getting their vaccine today would not be getting the protection they might expect until the middle of January. But some additional information has emerged on Pfizer’s vaccine that indicates that, while a single shot doesn’t provide full protection, it can still provide “pretty good” protection in the interim.
A series of new documents published by the FDA detail plans for the FDA’s Vaccines and Related Biological Products Advisory Committee scheduled for Thursday. The specific purpose of that meeting is to discuss whether the FDA will issue an emergency use authorization (EUA) for Pfizer’s vaccine. That EUA would open the door to begin administering the first doses of the vaccine in the U.S.
Included in those plans is a briefing document on the Pfizer vaccine that gives some information that hasn’t been seen before, or at least, not quite in this way.
Secondary efficacy analyses suggested benefit of the vaccine in preventing severe COVID-19, in preventing COVID-19 following the first dose, and in preventing COVID-19 in individuals with prior SARS-CoV-2 infection, although available data for these outcomes did not allow for firm conclusions.
So it appears that while one dose doesn’t provide full efficacy, the data did suggest that it was enough to help prevent the development of severe, life-threatening COVID-19. The second statement—that the first dose appeared to prevent reinfection of those who had already had COVID-19—is problematic in so many ways, in part because just one part of Pfizer’s trial considered volunteers whose blood showed SARS-CoV-2 antibodies at the outset, and because disentangling the effects of the vaccine from the effects of the disease itself would seem to demand a much larger pool of data.
The news most likely to generate headlines is that the secondary analysis indicates the Pfizer vaccine provided a fairly good level of protection from COVID-19 shortly after the first dose. The calculated efficacy was 52%, compared to the roughly 94% rate of the vaccine overall. That level of protection may not seem that great, but it’s actually much better than the flu vaccine in many years. In comparison, flu vaccines have ranged from a high of 60% in 2011 to a low of 10% in 2003. Over the last 17 years, the average efficacy of the flu vaccine has been around 40%.
The FDA had already announced that the value it was hoping to find in a COVID-19 vaccine was “above 50%.” That both Pfizer and Moderna actually achieved a level of protection > 90% is genuinely amazing—and an enormous boost to the mRNA technology where both companies bet big. Both Pfizer’s partner BioNTech and Moderna actually developed their vaccine within a week after the genetic sequence of the SARS-CoV-2 virus was published in January. Those are the vaccines approaching release now.
The fact that Pfizer’s vaccine appears to be reasonably effective after just one dose is great, and should help to reduce cases in the number of patients who will, inevitably, believe they are immune following the first dose, or even fail to return for a second. But the more important information in the briefing document is that the FDA review already seems to have found the Pfizer vaccine safe and effective.
“...based on the totality of scientific evidence available, it is reasonable to believe that the Pfizer-BioNTech COVID-19 Vaccine may be effective in preventing COVID-19 in
individuals 16 years of age and older, and the known and potential benefits of the Pfizer-BioNTech COVID-19 Vaccine outweigh its known and potential risks for use in individuals 16 years of age and older.”
It seems reasonable to believe that, barring any last-minute discovery, the FDA will issue an EUA for Pfizer’s vaccine soon after the meeting on Thursday.