factcheck.org

Q: How do people who have not been vaccinated against COVID-19 pose a risk to people who have been vaccinated? A: An unvaccinated person who is infected with COVID-19 poses a much greater risk to others who are also unvaccinated. But vaccines are not 100% effective, so there is a chance that an unvaccinated person could infect a vaccinated person — particularly the vulnerable, such as elderly and immunocompromised individuals.