Israel has begun giving a third dose of the COVID-19 vaccine developed by Pfizer (PFE -0.21%) and BioNTech (BNTX 2.06%) to some adults. The decision was made after COVID-19 cases began to surge in the country due to the spread of the delta variant.

The delta variant isn't just affecting Israel, though. It's now the most prevalent coronavirus strain in the U.S., causing 58% of all COVID-19 cases.

While Israel bought large quantities of the Pfizer-BioNTech vaccine, the U.S. has purchased hundreds of millions of doses of several COVID-19 vaccines. The two most widely given vaccines in the U.S. are those sold by Pfizer and Moderna (MRNA 5.66%).

Could the U.S. soon follow in Israel's footsteps? Are booster doses of Pfizer's and Moderna's COVID-19 vaccines on the way?

Healthcare professional giving a shot to a person.

Image source: Getty Images.

Not so fast

The U.S. Centers for Disease Control & Prevention (CDC) and U.S. Food and Drug Administration (FDA) have an answer about the need for booster doses for now. The two agencies issued a joint statement on July 8 that said: "Americans who have been fully vaccinated do not need a booster shot at this time."

So far in the U.S., nearly all COVID-19 hospitalizations and deaths have been with people who didn't receive a vaccine. Two doses of the Pfizer-BioNTech or Moderna vaccines (or one dose of Johnson & Johnson's single-shot vaccine) appear to provide ample protection against severe COVID-19. 

Even in Israel, not everyone is receiving a third booster dose of the Pfizer-BioNTech vaccine. The country's Health Ministry chose to only give the booster doses to severely immunocompromised individuals for now. This group includes organ transplant recipients and patients with cancer, multiple sclerosis, rheumatological, or autoimmune diseases.

And not all of these individuals should necessarily receive the third shot, according to the Israeli Health Ministry. The agency told healthcare providers via a public statement that most cancer patients won't need a booster dose. 

Boosting the boosters

Meanwhile, Pfizer, BioNTech, and Moderna believe that booster doses will be needed. Pfizer and BioNTech released a public statement on July 8 that noted findings from an Israeli real-world study that found decreasing efficacy for their vaccine due to the delta variant. The companies said: "We continue to believe that it is likely, based on the totality of the data we have to date, that a third dose may be needed within 6 to 12 months after full vaccination."

Moderna has also publicly voiced its belief that booster doses could be required. In the company's first-quarter conference call in May, CEO Stéphane Bancel said: "We have said for right now that we believe booster shots will be needed as we believe that the virus is not going away."

The companies are taking the rise of new coronavirus variants very seriously. Pfizer and BioNTech hope to win U.S. Emergency Use Authorization (EUA) for a third booster dose to more effectively protect against the delta variant. 

Perhaps the best path forward, though, is a vaccine that specifically targets the delta variant. Pfizer and BioNTech plan to begin clinical testing of a delta-variant-specific vaccine in August. Moderna is evaluating a multivalent booster vaccine candidate.

Why it matters for investors

The possibility that a third booster dose could be needed obviously matters to Americans who want to minimize the likelihood that they are diagnosed with COVID-19. It also matters to investors interested in Pfizer, BioNTech, and Moderna.

Each of these vaccine stocks could move higher if booster doses are needed to combat the delta variant. The requirement for additional doses would translate to increased sales for the companies. 

Booster doses might not be in the cards for all Americans, though. Even if the U.S. opts to authorize a third dose, it could choose to do so only for immunocompromised individuals in a manner similar to what Israel has already done. 

The bottom line, for now, is that it's too soon to count on booster doses boosting the shares of Pfizer, BioNTech, and Moderna. However, it's also too soon to discount the possibility.