Effectiveness of the 2010/11 seasonal trivalent influenza vaccine in Spain: preliminary results of a case-control study.

We present preliminary results of a case-control study to estimate influenza vaccine effectiveness in Spain, from week 50 of 2010 to week 6 of 2011. The adjusted effectiveness of the vaccine in preventing laboratory-confirmed influenza due to any type of influenza virus was 50% (95% CI: -6 to 77%) for the trivalent seasonal vaccine and 72% (95% CI: 7 to 92%) for both trivalent seasonal and monovalent pandemic vaccines, suggesting a protective effect of seasonal vaccination lower than that reported for the previous season.