What is a booster? “The simplest answer is that it's just another dose of a vaccine you received,” Dr. Shaw explains. “The concept is to prolong protective immunity, particularly if there is evidence that protection is waning after a period of time.”

What does a booster shot do?

Typically, you would get a booster after the immunity from the initial dose(s) naturally starts to wane. The booster is designed to help people maintain their level of immunity for longer.

Do COVID-19 vaccine boosters work?

Results from Israel indicate that a booster dose greatly lowers the risk of severe illness. Boosters also prevent infection. This reduces the spread of SARS-CoV-2 among vaccinated and unvaccinated individuals. It isn't yet clear how long protection from boosters will last, but the world can't wait to find out.