What happened

For the second straight day, the share price of otherwise popular coronavirus stock BioNTech (BNTX -0.45%) fell on Tuesday. Despite there being no direct catalysts for such a drop, the shares of the German company ended the day nearly 3.5% lower.

So what

BioNTech is, it nearly goes without saying by now, the co-developer of the Comirnaty coronavirus vaccine with pharmacuetical sector powerhouse Pfizer (PFE -0.19%). The jab is the only one fully approved for use in the U.S.; vaccines from Moderna and Johnson & Johnson's Janssen currently hold only Emergency Use Authorization (EUA).

Child wincing as he receives a vaccination shot.

Image source: Getty Images.

Both BioNTech and Pfizer shares slipped on Monday and Tuesday, which doesn't feel like a coincidence. Their sell-offs instead appear to be part of a wider trend of investors either taking profits on the stocks, and/or vacating their positions in favor of titles seen to have more potential in a (fingers crossed) post-pandemic world.

Both companies saw their share prices rise precipitously, more or less in line with the exploding popularity and widespread use of Comirnaty following the Food and Drug Administration's initial granting of an EUA for the vaccine in December 2020. But lately, as the world has occasionally glimpsed light at the end of the long coronavirus tunnel, the two stocks have slipped from investor favor somewhat.

Now what

This sentiment is potentially more damaging to BioNTech than it is to Pfizer. The American company operates a sprawling business with a solid lineup of commercial treatments in numerous categories and a wide pipeline. The relatively young European biotech, on the other hand, has only one product on the market and a far smaller set of treatments in development.