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.
• Protect against influenza A (H1N1), influenza A(H3N2), and influenza B viruses.
• Protect different age groups from flu.
• Protect special populations from flu.

CDC uses VE estimates in multiple ways:

• To estimate the number of illnesses, hospitalizations and deaths caused by influenza.
  See Disease Burden of Influenza for more information.
• To estimate the number of flu-related illnesses, hospitalizations and deaths averted through vaccination.
  See Estimated Influenza Illnesses, Medical visits, and Hospitalizations Averted by Vaccination for more information.

• To inform the annual selection of vaccine viruses for the following season’s Northern Hemisphere flu vaccine. See Past Meeting Materialsexternal icon for examples of this.
• To inform the annual influenza vaccination recommendations. See the Methods section of the recommendations for more information.
• VE estimates also inform the development of improved vaccine technologies.
  See Influenza Vaccine Advances for more information.

Researchers also have used the Flu VE Network to conduct evaluations on specialized influenza topics such as:

•  assessing risk of influenza by birth cohorts
• immunity based on serological evidence
• use of influenza antiviral drugs to treat influenza
• providers’ antibiotic prescribing habits during flu season
• flu vaccine effectiveness following repeat vaccination
• duration of influenza vaccine protection
• vaccine effectiveness of pandemic flu vaccines
• genetic characteristics of flu viruses and VE by genetic groups of viruses