- Pfizer and BioNTech on Thursday released new results from the large, international study that led to U.S. authorization of their coronavirus vaccine last year, showing the shot's protective effects appear to hold up for at least six months.
- The updated data comes from an analysis of 927 symptomatic COVID-19 cases that occurred in the study through March 13. Pfizer's vaccine remained 91.3% effective and offered near-complete protection against severe disease. Notably, there were no cases among hundreds of vaccinated participants in South Africa, where a variant that can weaken vaccine potency was first detected.
- The results give a better sense of how long the protection offered by Pfizer's shot holds up, an important question that could determine when or whether booster shots will be necessary. The data should also allow Pfizer to file for full approval of its shot in the U.S., where it's currently only cleared for emergency use.
Though Pfizer and rival Moderna's vaccines have proven remarkably effective and safe in both clinical testing and real world use, they were each authorized under a clearance reserved for public health crises.
That pathway, known as emergency use authorization, enabled both shots to get to market faster than they would otherwise. Pfizer's vaccine, for instance, was authorized after 170 volunteers developed symptomatic COVID-19 in its Phase 3 trial and after just two months of safety follow-up were available for half of the study participants. At the time, Pfizer reported its vaccine was 95% effective at preventing COVID-19 in the trial.
But those speedy authorizations meant there were still outstanding questions only time could answer, such as how long protection would last or whether rare side effects would crop up later. Both Pfizer and Moderna needed to collect more data to convert their authorizations into full approvals that would last beyond the immediate pandemic emergency.
And as both shots were tested last year, it's unclear if they're similarly protective against new virus variants — especially B.1.351, which was first found in South Africa and is more resistant to vaccination. Johnson & Johnson and Novavax's vaccines, evaluated afterwards, were less effective against B.1.351 than other strains, and AstraZeneca's shot provided little protection in a small trial.
Those findings have raised concerns B.1.351 might drive "breakthrough" infections in people vaccinated with Pfizer's and Moderna's shots, too. Out of caution, both drugmakers have begun to test boosters and variant-specific shots. A first-of-its-kind National Institutes of Health-sponsored study of a Moderna shot tailored to B.1.351 began on Wednesday. A study testing a third shot of Pfizer's original vaccine is underway as well.
All of which makes the new data Pfizer disclosed Thursday — the first time a drugmaker has reported six months of follow-up for a coronavirus vaccine — important. Pfizer said that 927 symptomatic COVID-19 cases have now occurred among study participants. Eight hundred and fifty were in the placebo group versus 77 among those who were immunized — a 91.3% efficacy rate.
Thirty-two cases of severe disease have occurred in the trial. Only one was in a vaccinated person, though that case isn't considered "severe" under a definition used by the Centers for Disease Control and Prevention.
Pfizer said that among 800 participants enrolled in South Africa, nine COVID-19 cases occurred, six of which were caused by B.1.351 infections. None of those volunteers had received the vaccine, suggesting the shot may protect against the troublesome variant, though it's difficult to draw conclusions because the sample size is small.
Both Pfizer and Moderna have said they expect their shots to neutralize B.1.351 despite lab tests showing weaker immune responses against it than for the original coronavirus strain. But both have also indicated they expect booster shots will be necessary to maintain protection.
"Boosters at six months against the variant likely remains a priority," wrote Umer Raffat, an analyst at Evercore ISI, in a note on Thursday.
Importantly, no new safety problems have emerged after the vaccination of more than 44,000 trial volunteers, including more than 12,000 who are six months removed from their second shot. The results "position us to submit [an approval application] to the FDA," Pfizer chairman and CEO Albert Bourla said in a statement.
Pfizer said it will publish detailed study results in "the near future."