Booster Shots Are Safe and Effective

UPDATE: On Nov. 19, FDA amended the emergency use authorizations (EUA) for both the Moderna and Pfizer-BioNTech COVID-19 vaccines authorizing use of a single booster dose for all individuals 18 years of age and older after completion of primary vaccination with any FDA-authorized or approved COVID-19 vaccine.

Since the introduction of the vaccines, scientists have acknowledged that booster shots would be likely either to deal with new variants or to combat waning immunity. The FDA recently authorized additional doses for all three COVID-19 vaccines.

Available data show that booster shots are safe and effective, which led the FDA to authorize an additional dose of the Pfizer vaccine for certain groups in late September and an additional dose of the Moderna vaccine for certain groups in October. Those boosters can be administered at least six months after completion of the first series. FDA also authorized an additional dose of the Johnson & Johnson vaccine; anyone 18 and older who initially got that vaccine is eligible for a booster at least two months after completion of the first shot, reflecting lower levels of protection from the initial single dose. FDA also indicated that people can get a different shot from the one they first received. Those eligible for boosters of Pfizer or Moderna include people 65 and older, and people 18 through 64 who are either at high risk for severe disease or living or working in high-risk situations with exposure to SARS-CoV-2.

Data from Israel, which vaccinated its population early and quickly, indicate that protection against the SARS-CoV-2 virus decreases six months post vaccination. Boosters reduce the risk of severe illness and prevent infections, reducing the spread of the virus. This increases protection for vaccinated and unvaccinated people, immunocompromised people, and people with underlying health conditions.

Another question that the FDA addressed was the use of heterologous boosters. A preprint published last week indicates that mixing vaccines is safe and effective, although by in large there was not enough data to indicate if any specific combination of vaccines was more effective. It appears that for those that got the Johnson & Johnson vaccine as their first shot, the mRNA vaccines are most beneficial. For those who got either of the mRNA vaccines first, both Pfizer and Moderna boosters seem to be about equal, with a Johnson & Johnson booster providing moderate benefit.

The take home message from all of this is that boosters are safe and effective and that you can likely take whichever one is available to you. This should make it easier for eligible people to get a booster.

Dr. Pfister is assistant professor at the University of Massachusetts Medical School and chair of the ASGCT Communications Committee.