Reduced serologic sensitivity to influenza A virus illness among inactivated influenza vaccinees

We compared ≥4-fold increases in antibody titers by hemagglutination inhibition assay to RT-PCR results among 42 adults with PCR-confirmed influenza A virus illnesses. Serologic sensitivity was higher among unvaccinated (69%, 95% confidence interval [CI] = 48-90%) than vaccinated healthcare personnel (38%, 95% CI = 29-46%) in a 2010-11 prospective cohort.