There are a few reasons why people who are vaccinated continue to get COVID-19. For one, no vaccine is 100% effective at preventing infection, and highly contagious variants have led to breakthrough infections among vaccinated people. Also, the level of protection from the vaccine decreases over time, leading to less protection against the virus. Ultimately, as the total number of vaccinated people increases, the pool of unvaccinated people gets smaller—that means proportionally, more cases will be among the vaccinated.
While vaccines are developed in part to prevent infection from disease, the main goal of vaccines is to prevent severe illness or death. The COVID-19 vaccines continue to be highly effective in reducing risk of severe disease, hospitalization, and death, and can provide sustained protection when you receive a booster dose. When COVID-19 cases rise, breakthrough infections among vaccinated individuals are significantly more likely to be mild cases, while unvaccinated people are more likely to become severely ill or require hospitalization. CDC data show that through December 25, 2021, the risk of being hospitalized with COVID-19 in the U.S. was 16 times greater for unvaccinated adults than fully vaccinated adults.
Updated February 18, 2022