With more contagious variants of the COVID-19 virus spreading just as people are starting to feel comfortable reentering society, talk about the benefit of vaccine boosters is amping up.
Pfizer is seeking approval for a third dose of its vaccine, given as a booster, and some countries, including Britain and Israel, have already said they will boost vulnerable populations.
Yet the U.S. Centers for Disease Control and Prevention and the Food and Drug Administration have said boosters are not currently necessary for fully vaccinated Americans.
We talked to the University of Pennsylvania's Drew Weissman, an immunologist who helped develop the messenger RNA concept behind Pfizer's vaccine, to unpack the international argument about COVID-19 boosters.
What is a booster shot?
Vaccines cause our bodies to develop antibodies to protect against a virus. A booster shot is an extra dose that "boosts" immunity by spurring the development of more antibodies.
There are two types of booster shots: The first kind is a follow-up dose that is identical to the initial vaccine, such as the tetanus booster recommended every 10 years. Other vaccine boosters are tweaked from their original form to protect against a new variant. A common example is the influenza vaccine, which is slightly different each season to target the most common current strain of the flu virus.
The type of boosters developed for COVID-19 may vary. A follow-up dose of the original vaccine would have a faster path to regulatory approval, since vaccine makers have already received emergency use authorization. Tweaked versions of the COVID-19 vaccines could be useful in targeting variants, especially if a variant emerges against which the current vaccines are not effective. No such variant has come about yet — the vaccines have proven effective against the delta and other new variants.
Will booster shots be necessary for the COVID-19 vaccine?