What to know
- CDC’s Vaccine effectiveness (VE) estimates measure different kinds of benefits, like prevention of flu-related doctor’s visits, hospital visits, and intensive care unit (ICU) admissions.
- VE is also measured in different age groups and against specific types and subtypes of influenza viruses that spread each year.
- CDC calculates flu vaccine effectiveness (VE) for multiple public health reasons, such as to inform estimates of flu disease burden and burden prevented by vaccination and to help inform annual flu vaccination recommendations.
CDC’s VE estimates describe a vaccine’s ability to:
- Prevent flu-related trips to the doctor
- Prevent severe flu illness requiring hospitalization or intensive care unit (ICU) admission
- Protect against influenza A (H1N1), influenza A(H3N2), and influenza B viruses
- Protect people in different age groups from flu, including children and older adults
- Protect people in higher risk groups, including pregnant people and people with certain chronic health conditions, from getting sick with flu
CDC uses VE estimates in multiple ways:
- To estimate the number of illnesses, hospitalizations and deaths caused by flu.More information is available at Disease Burden of Influenza.
- To estimate the number of flu-related illnesses, hospitalizations and deaths that are averted through vaccination.More information is available at Estimated Influenza Illnesses, Medical visits, and Hospitalizations Averted by Vaccination.
- To inform the annual selection of vaccine viruses for the following season's Northern Hemisphere flu vaccine. Examples from past flu seasons are available at Past Meeting Materials.
- To inform the annual flu vaccination recommendations. More information is available in the Methods section of the recommendations.
- VE estimates also inform the development of improved vaccine technologies. More information is available at Influenza Vaccine Advances.
Researchers also have used the Flu VE Network to conduct evaluations on specialized flu topics such as:
- assessing risk of flu by birth cohorts
- immunity based on serological evidence
- use of flu antiviral drugs to treat flu illness
- providers' antibiotic prescribing habits during flu season
- flu vaccine effectiveness following repeat vaccination
- duration of flu vaccine protection
- vaccine effectiveness of pandemic flu vaccines
- genetic characteristics of influenza viruses and VE by genetic groups of viruses