Since the first people in the COVID-19 vaccine clinical trials were vaccinated at the end of July 2020 and the first vaccines were approved in December 2020, we only have information about protection against disease for a few months after vaccination. The phase 3 trials have not finished yet for all vaccines and trial participants will continue to be monitored, so we will learn more, but we do not yet know whether booster doses will be needed. Based on the elements of the immune response activated after vaccination with either the mRNA or adenovirus vaccines, it is likely that immunity will be long-lived. Furthermore, the increasing presence of variants might affect whether or how often additional doses would be needed. Scientists are continuing to monitor variants and the ability of currently available vaccines to protect against them.