Why CDC Estimates Vaccine Effectiveness (VE)

CDC calculates flu vaccine effectiveness (VE) for multiple reasons.

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 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: