A live attenuated influenza A(H1N1)pdm 2009 vaccine was developed and distributed in India in 2010. We estimated the vaccine effectiveness (VE) against laboratory-confirmed pandemic H1N1 (pH1N1) infections in patients with influenza-like illness who visited five tertiary care hospitals in Pune, India during June-December 2010. Swab specimens were analyzed for influenza pH1N1 by reverse transcriptase polymerase chain reaction (RT-PCR). VE was estimated using the test-negative case-control study design and logistic regression. A total of 784 patients (253 cases, 531 controls) were analyzed. The unadjusted overall VE was 75.5% (95% confidence interval [CI] 42.1-89.7), while the adjusted VE was 76% (95% CI 42.1-89.7). We conclude that the live attenuated influenza A(H1N1)pdm 2009 vaccine was effective in our study population, which has opened prospects for using this platform for trivalent formulations.
Keywords: case control; effectiveness; influenza A(H1N1)pdm 2009; live attenuated vaccine; pandemic.