COVID-19 vaccination will protect most people from getting sick with COVID-19. But some people who are up to date with their vaccines may still get COVID-19. These are called vaccine breakthrough infections.

People with vaccine breakthrough infections can spread COVID-19 to others. However, people who are up to date with their vaccines but who have a breakthrough infection are less likely to have serious illness with COVID-19 than those who are not vaccinated. Even when people who are vaccinated get symptoms, they tend to be less severe than those felt by unvaccinated people.

Researchers continue to study what happens when someone has COVID-19 a second time. Reinfections and breakthrough infections are generally milder than the first infection. But severe illness can still happen. Serious illness is more likely among people older than age 65, people with more than four medical conditions and people with weakened immune systems.