What happened

Shares of BioNTech (NASDAQ:BNTX) soared 21.3% this week as of the market close on Thursday. Moderna (NASDAQ:MRNA) and Novavax (NASDAQ:NVAX) stocks also both jumped 12.4% this week.

The common denominator driving all three vaccine stocks higher was increased concern about the delta variant of the coronavirus. COVID-19 cases in the U.S. and several other countries across the world are rising due to the highly contagious strain. The Centers for Disease Control and Prevention (CDC) said earlier this week that the delta variant now accounts for 83% of new COVID-19 cases in the U.S.

There was also other news driving a couple of the stocks higher. BioNTech and its partner, Pfizer (NYSE:PFE)announced a letter of intent with Biovac to produce COVID-19 vaccines for distribution to 55 member countries of the African Union. Moderna announced new supply deals with Japan and Taiwan. 

Street signs with "COVID-19" and "Delta" printed on them and dark clouds in the background.

Image source: Getty Images.

So what

Although worries about the delta variant primarily fueled the gains for BioNTech, Moderna, and Novavax this week, it remains to be seen what impact the variant will actually have on the companies' fortunes. The CDC and the U.S. Food and Drug Administration (FDA) maintain that current vaccines on the market offer strong protection against severe cases of COVID-19, even ones caused by the delta variant.

One study published in the New England Journal of Medicine on Wednesday seemed to back up the CDC-FDA stance for a couple of COVID-19 vaccines. The study found that the Pfizer-BioNTech vaccine and AstraZeneca's vaccine (which hasn't received Emergency Use Authorization in the U.S. yet) are almost as effective against the delta variant as they are against the alpha variant first identified in the U.K. The Pfizer-BioNTech vaccine was 88% effective at preventing symptomatic COVID-19 caused by the delta variant, only a little lower than the vaccine's 93.7% efficacy against the alpha variant. 

However, real-world data from Israel announced earlier this month wasn't so encouraging. Israel's Health Ministry stated that the Pfizer-BioNTech vaccine's efficacy fell to 64% from an earlier efficacy of 95.3% when the delta variant wasn't prevalent.

How the vaccines fare against the delta variant is important in part because of what it could mean for the need for third booster doses. If booster doses are required, sales for authorized vaccines could be even higher than what is currently projected.

Now what

Look for BioNTech (along with Pfizer) and Moderna to keep picking up more deals to supply doses of their COVID-19 vaccines in 2022. Both companies also should continue to build their cash stockpiles and could put the money to use through acquisitions and licensing agreements to bolster their pipelines.

For Novavax, the major milestone ahead is the company's anticipated filing for Emergency Use Authorizations (EUAs) for its COVID-19 vaccine in the U.S., U.K., and European Union later this quarter. Novavax has already reported positive results from late-stage studies of its vaccine that should bode well for its chances of winning EUA.

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.