Why Pfizer stock fell on Friday

In the midst of the coronavirus pandemic a few years ago, any positive news from a developer of vaccines or drugs for COVID-19 would have been met with a wave of buying of its stock. However, we are no longer in 2021 and an encouraging development from Pfizer (PFE -1.43%) on a combination COVID/flu jab was met with a collective shrug by the market. In fact, investors traded out of the stock to the point where its price fell 1.4%, compared to the stock’s 0.2% rise. S&P 500 index of the day.

The combination vaccine is insufficient in clinical trials

Before the market opened, Pfizer and BioNTechco-developer of his wildly popular Comirnaty COVID, has released an update on that combination vaccine.

A phase 3 clinical trial involving patients aged 18 to 64 met one of its two primary objectives, with the combination vaccine successfully achieving immunogenicity against the SARS-CoV-2 strain of the virus that causes COVID. However, it failed to do so for both influenza A and influenza B, producing an insufficient immune response for the latter. In their joint press release, the companies quoted Pfizer’s head of vaccine research, Annaliesa Anderson, as saying:

We are committed to developing vaccines that will reduce the burden of respiratory disease, and we believe that combination vaccines are the most effective way to do this. Today’s results provide insight and direction toward achieving that goal, and we remain optimistic about our combined COVID-19 and influenza program, for which we are evaluating next steps.

Back to the drawing board

The modest selloff indicated that investors, like the two companies, see enough positives in the late-stage trial to not give up hope on the combination vaccine. COVID is still a threat and the flu is a constant health scourge. So if Pfizer and BioNTech can finally develop an effective two-for-one punch, it would almost certainly prove to be a very popular jab.