This study reports effectiveness of trivalent influenza vaccine (TIV) against confirmed pandemic influenza infection in England using a retrospective test-negative case-control study. Cases and controls were frequency matched by age, swabbing-week and region. On univariable and multivariable analysis adjusted for underlying clinical risk factors, cases were no more or less likely than controls to be vaccinated with 2008-09 or 2007-08 season TIV. Adjusted vaccine effectiveness for the former was -6% (-43% to 22%). Vaccine effectiveness did not differ significantly by age-group or hospitalisation status. There was no evidence prior vaccination with TIV significantly altered subsequent risk of pandemic influenza H1N1 2009 infection.
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