In this Jan. 15, 2021, file photo, Dr. Yomaris Pena, Internal Medicine Physician with Somos Community Care extracts the last bit of Pfizer COVID-19 vaccine out of a vial at a vaccination site at the Corsi Houses in the East Harlem neighborhood of New York. Credit: Mary Altaffer / AP

Tens of thousands of Mainers are now eligible for COVID-19 booster shots after the U.S. Centers for Disease Control and Prevention authorized them last week to provide an extra layer of protection for people whose immunity may be waning.

But eligibility for the shots depends on a number of factors, including what vaccine you initially received, how long it has been since then and your age and other risk factors. Use the quiz below to see if you are eligible right now.