Evaluation of inter-pandemic influenza vaccine effectiveness during eight consecutive winter seasons in England and Wales in patients with cardiovascular risk factors

We evaluated the effectiveness of inactivated influenza vaccine in persons aged >/= 45 years with co-morbidities [including essential hypertension] likely to have prompted consideration of prophylactic statin therapy. Using case-control analyses, we measured the impact of vaccination on General Practitioner [GP] reported new episodes of illness for clinically diagnosed influenza-like illness [ILI] and total acute respiratory infection [TARI] during eight consecutive winters, adjusting for potential confounders using multivariable techniques. Although the study failed to demonstrate the effectiveness of influenza vaccine, we identified important potential confounding related to a greater likelihood of vaccinees than non-vaccinees to consult with a GP for respiratory infections. Future researchers should consider and account for this phenomenon