Test-Negative Design: The Importance of Laboratory-Confirmed Illness in Estimating the Effectiveness of Influenza Vaccine in Older Adults.

The article examines the significance of laboratory-confirmed illness for an effective estimation of influenza vaccine in older adults in many countries worldwide. An overview on the observational studies on the result of influenza in the U.S., is provided. Challenges in Cochrane methods for influenza vaccine analysis, is also cited.