Another major influence on vaccine effectiveness is the amount of community transmission of the virus. That can be affected by changes in behavior, such as engaging in riskier activities. If a vaccinated person is in a community where lots of people are not wearing masks and are breathing out the coronavirus in crowded indoor settings — offering more chances for the virus to spread — effectiveness against infection can be lower than it is for a person who lives where people are more cautious and the virus is rarer.

Source: Washington Post August 17, 2021 20:48 UTC