We present immunogenicity data on the routine vaccination of 103 health care personnel during the 2009 H1N1 national vaccination campaign. The seroprotection rate (percentage of samples with hemagglutination inhibition titers of ≥1:40) was 83.2% at 30 days postvaccination, lower than those obtained in previously published controlled trials. Low baseline antibody levels and an increase in seroprotection in a negative-control cohort suggest that the virus remains prevalent.
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