Why CDC Estimates Vaccine Effectiveness (VE)

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

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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:

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 flu viruses and VE by genetic groups of viruses