Assessment of seasonal influenza vaccine effectiveness in patients from a central Italy reference hospital: Pitfalls and intricacies from a pilot case-control study

Background: Influenza vaccination protects high-risk populations from severe outcomes.Methods: During the 2011-2012 flu season at "Gemelli Hospital" in Rome, all hospitalised patients who developed suspected influenza-like illness within 14 days were recruited to assess the feasibility of testing the influenza vaccine effectiveness against laboratory-confirmed influenza requiring hospitalisation.Conclusions: No difference in vaccine status between patients with positive and negative laboratory tests was found due to the small sample size. Larger numbers are required to explore influenza vaccine effectiveness.Results: Sixty-two patients were recruited; among them, 18 were laboratory confirmed for influenza A or B. In the target group for vaccination (N=47), the prevalence of vaccinated subjects was less than expected (38%).