What happened

A monster revenue miss was the big reason for the widespread investor sell-off in BioNTech (BNTX -3.29%) stock on Monday. As of late-session trading that day, the once-hot biotech's share price had fallen by more than 7%. Meanwhile, in contrast, the S&P 500 index was in positive territory, rising by nearly 0.8%.

So what

For its second quarter, BioNTech posted total revenue of 167.7 million euros ($184.5 million). That was very much down from the nearly 3.2 billion euros ($3.5 billion) it earned in the same period of 2022. The dynamic was similar on the bottom line, with the biotech flipping to a loss of more than 190 million euros ($209 million) from the year-ago profit of almost 1.7 billion euros ($1.9 billion).

The reason for the dramatic change wasn't hard to tease out. The one commercialized product that put BioNTech on the map, Comirnaty (developed in partnership with Pfizer), is a COVID vaccine. With the general waning of the coronavirus pandemic, demand for the shot fell off a cliff.

That being said, analysts were broadly expecting BioNTech to land in the red. In fact, they were modeling a deeper deficit -- 0.83 euros ($0.91) per share -- than the company actually posted. Its per-share loss for the period was 0.79 euros ($0.87).

Now what

In its earnings release, BioNTech reiterated its revenue guidance for the entirety of 2023. It believes it will earn roughly 5 billion euros ($5.5 billion) on its share of Comirnaty sales.

It did lower its forecasts for certain cost items, including research and development expenses. These are now expected to total 2 billion euros ($2.2 billion) to 2.2 billion euros ($2.4 billion); previously, the company was modeling 2.4 billion euros ($2.6 billion) to 2.6 billion euros ($2.9 billion).