What happened

Shares of BioNTech (NASDAQ:BNTX) were sinking 6.2% lower as of 3:33 p.m. EDT on Monday. The decline appeared to result from speculation by Bernstein biotech analyst Vincent Chen that the coronavirus vaccine candidate BNT162b2 developed by BioNTech and its partner Pfizer (NYSE:PFE) could have lower efficacy than expected. 

So what

Chen thinks it's likely that BioNTech and Pfizer have had two interim analyses from the late-stage study of BNT162b2 already. The partners have publicly stated that preliminary efficacy results could be announced in October. Because the companies haven't announced any data yet, Chen suspects that the vaccine could have had a lower efficacy than initially hoped.

Physician giving a shot in a person's arm

Image source: Getty Images.

However, there are plenty of other reasons why the companies might have opted to hold off on announcing preliminary late-stage efficacy results. For example, Pfizer provides its third-quarter update on Tuesday morning. It's possible that the big drugmaker wanted to wait to report the results for BNT162b2 at the same time. 

The bottom line is that at this point any discussion of the efficacy of BNT162b2 is purely speculation. And as long as the vaccine doesn't have worrisome safety issues, an efficacy of 50% or more will be enough to win FDA emergency use authorization.

Now what

We should soon know how well BioNTech's experimental coronavirus vaccine is faring in late-stage studies one way or another. In the meantime, the biotech stock will likely remain relatively volatile -- especially with increased choppiness in the overall stock market.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.