Pfizer and its partner BioNtech released new safety and efficacy data for their coronavirus vaccine Wednesday, and said it shows protection holds up for at least six months, although it may start to wane slightly towards the end of that time.
The pre-print paper, posted Wednesday to the online server medrxiv.org, updates results from Pfizer’s trial involving 44,000 volunteers around the world.
It found the overall efficacy was about 91% during the six months. Vaccine efficacy against severe Covid-19 was about 97%, the data show. The paper has not yet been peer-reviewed nor published in a journal.
Some more details: The data show that the vaccine’s efficacy peaked at more than 96% from a week to around two months after receiving a second dose of vaccine, and then appeared to gradually decline to 83.7% four to six months later, with an average decline of about 6% over the last two months.
The Pfizer/BioNTech vaccine — administered as two doses 21 days apart — was authorized in December and at the time data were unavailable beyond two months after vaccinations. The data at the time — which are now updated in the new pre-print paper — were submitted to the US Food and Drug Administration to authorize the vaccine.
The data now show that, despite a “gradually declining trend in vaccine efficacy,” the vaccine was still “highly efficacious” in preventing Covid-19 and had a favorable safety profile six months later.
It was not clear why efficacy seemed to drop off. The pandemic also changed over the course of six months, with the emergence of several variants.