What happened
Shares of BioNTech (BNTX +1.23%) were down 5.3% as of 10 a.m. EDT on Tuesday. Meanwhile, shares of Moderna (MRNA +2.74%) were slipping 2.7%.
There appear to be two common denominators between the declines of these two vaccine stocks. First, the overall stock market fell this morning. Second, the Israeli Health Ministry announced that the COVID-19 vaccine developed by Pfizer (PFE +0.29%) and BioNTech appears to be less effective against the Delta variant, a coronavirus strain that's spreading rapidly.
Image source: Getty Images.
So what
Many stocks fall when the overall market drops. However, the news from Israel appears to be causing the shares of BioNTech and Moderna to take a harder hit than many other stocks.
The Israeli Health Ministry stated that the Pfizer-BioNTech vaccine is 64% effective in preventing infection and symptomatic disease. That's a sharp decline from the vaccine's initially reported efficacy. The change appears to be related to the increase in the spread of the Delta variant.
Investors viewed this as especially bad news for BioNTech. All of the German biotech's revenue currently stems from sales of the COVID vaccine that it co-markets with Pfizer.
The data from Israel didn't address Moderna's COVID vaccine. However, the report was seen as potentially negative for Moderna because its vaccine, like the Pfizer-BioNTech vaccine, is based in messenger RNA (mRNA) technology.
There was some good news with the Israeli Health Ministry announcement, though. The Pfizer-BioNTech vaccine was 93% effective in preventing hospitalizations and serious illness, close to its previously reported efficacy levels.
Now what
The Pfizer-BioNTech and Moderna teams are conducting clinical studies of booster doses that target coronavirus variants. With the lower efficacy reported from Israel, the results from these studies could be even more important to the companies' fortunes.
