We aimed to estimate the effectiveness of H1N1/09 containing influenza vaccines against hospitalization from influenza in Australia. We performed a test-negative case control study in patients hospitalized in 15 sentinel Australian hospitals between March and November 2010, comparing influenza vaccination (H1N1/09 monovalent or 2010 seasonal trivalent) in hospitalized patients with PCR-confirmed influenza compared to PCR-negative controls. Between March and November 2010, 1169 hospitalized patients were tested for suspected influenza, of which influenza vaccine status was ascertained in 165/238 patients with H1N1/09 influenza, 40/64 with seasonal influenza and 558/867 test negative controls; 24% of H1N1/09 cases, 43% of seasonal influenza cases and 54% of controls were vaccinated. VE against hospitalisation with H1N1/09 influenza after adjusting for age, medical comorbidities and pregnancy status was estimated at 49% (95% CI: 13%, 70%). Influenza vaccination was associated with a reduction in hospitalisation caused by H1N1/09 influenza in the 2010 southern hemisphere winter season.
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