Effectiveness of the trivalent influenza vaccine in Navarre, Spain, 2010-2011: a population-based test-negative case-control study.

Background Some studies have evaluated vaccine effectiveness in preventing outpatient influenza while others have analysed its effectiveness in preventing hospitalizations. This study evaluates the effectiveness of the trivalent influenza vaccine in preventing outpatient illness and hospitalizations from laboratory-confirmed influenza in the 2010–2011 season.