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Monitoring COVID-19 Vaccine Effectiveness
Why CDC Tracks How Well the Vaccines Are Working
CDC is reviewing this page to align with updated guidance.
CDC continuously monitors vaccine effectiveness to understand how COVID-19 vaccines protect people in real-world conditions.
Vaccine effectiveness is a measure of how well vaccination protects people against infection, symptomatic illness, hospitalization, and death.
CDC monitors COVID-19 vaccine effectiveness to understand how well the vaccines:
- Protect different age groups, such as children, adolescents, and adults, including adults ages 65 and older
- Protect specific groups, such as people with underlying health conditions or healthcare workers
- Protect against new variants
- Lower the risk of infection, including infection without symptoms
- Protect against milder COVID-19 illness
- Prevent more serious outcomes, such as hospitalization or death
- Prevent complications from COVID-19, such as post-COVID conditions and multisystem inflammatory syndrome (MIS)
- Prevent spreading COVID-19 to others
- Provide long- and short-term protection
- Perform among people who have received one or more booster doses
Assessing How Vaccines Work in the Real World Helps Us:
Adjust vaccine recommendations, as needed, such as booster doses
Guide vaccine policy and vaccine distribution
Inform development of vaccine technologies
COVID-19 Vaccines and New Variants of the Virus
Viruses are constantly changing to create new types of the virus, called variants. So far, research shows that the COVID-19 vaccines used in the United States continue to protect against severe disease, hospitalization, and death from known circulating variants. They may not be as effective in preventing infection from these variants. CDC will continue to monitor vaccine effectiveness to see what impact, if any, variants have on how well COVID-19 vaccines work in real-world conditions.
How CDC Monitors COVID-19 Vaccine Effectiveness
CDC uses multiple strategies to monitor how well COVID-19 vaccines are working in real-world conditions.
![Read MMWR COVID-19 vaccine effectiveness and safety reports](/congress117th/20221219232411im_/https://www.cdc.gov/coronavirus/2019-ncov/images/vaccines/mmwr.jpg?_=40922)