What happened

Shares of the leading COVID-19 vaccine makers received a modest bump today. Pfizer (PFE -0.38%) stock was up 1.5% as of 10:38 a.m. EDT on Friday. Shares of the company's partner, BioNTech (BNTX 2.05%), rose 2.2%. Moderna (MRNA 6.10%) stock was also up 2.1%.

There was a common catalyst for these vaccine stocks. The U.S. Food and Drug Administration announced Thursday evening that it had expanded the Emergency Use Authorizations for the Pfizer-BioNTech COVID-19 vaccine and the Moderna COVID-19 vaccine to include a third booster dose for immunocompromised individuals.

Healthcare professional giving a shot to a person.

Image source: Getty Images.

So what

The FDA specifically mentioned organ transplant recipients as being eligible for booster doses. The agency also said that individuals who are similarly immunocompromised could receive booster shots as well.

While this is good news for Pfizer, BioNTech, and Moderna, it likely won't move the needle very much in terms of sales. Acting FDA commissioner Janet Woodcock used the phrase "small, vulnerable group" to describe the individuals who would qualify for the booster doses. Most Americans won't be affected by the EUA changes.

Now what

Woodcock stated that the agency currently believes that individuals who aren't immunocompromised and are fully vaccinated "are adequately protected and do not need an additional dose of COVID-19 vaccine at this time." However, the FDA continues to review whether or not booster doses will be needed for more people in the U.S. 

Even if the FDA determines that booster doses are appropriate for the larger population, it might not have a huge impact on revenue for Pfizer, BioNTech, and Moderna. The U.S. has already ordered enough doses from the companies to provide booster shots for many Americans.