Babu TM, et al. - In order to evaluate the age-related frequency of current population immunity to H2 viruses, researchers performed hemagglutinin inhibition (HAI) assays against historical human and recent avian influenza A (H2N2) viruses across age groups in Rochester, NY and Hong Kong, China. Findings suggested insufficient population immunity to H2 viruses to block epidemic spread of H2 virus. Lower impact of H2N2 pandemic would be observed in those born before 1968.