We estimate the impact of the two previous influenza seasonal vaccines and the pandemic vaccine on risk of A (H1N1) 2009 laboratory confirmed hospitalizations during the autumn 2009 pandemic wave in Castellón, Spain. We conducted a test-negative, hospital-based, case-control study. Influenza A (H1N1) 2009 infection was detected in 147 (44%) of 334 patients hospitalized for a presumptive influenza related illness. No effect was observed for the 2008-2009 and 2009-2010 seasonal influenza vaccines. However, the pandemic vaccine was associated with an adjusted vaccine effectiveness of 90% (95% CI, 48-100%). Pandemic vaccines were effective in preventing pandemic influenza associated hospitalizations.
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