Effectiveness of influenza vaccination in reducing pneumonia and influenza hospitalizations and deaths among elderly members of a prepaid health plan was analyzed retrospectively. Two epidemics caused by the H3N2 subtype of type A influenza were studied. Vaccine derived from the H2N2 subtype of influenza A virus failed to protect against the Hong Kong (H3N2) virus during the 1968-1969 epidemic. Vaccine derived from the A/Hong Kong/68 (H3N2) virus yielded an estimated 72% (31% to 100%) reduction in hospitalization and 87% (52% to 100%) reduction in mortality during the 1972-1973 epidemic caused by A/England/72 (H3N2). These findings are consistent with those reported in vaccinated young persons, and hence it appears they may be broadly generalized.
Barker WH, Mullooly JP. Influenza Vaccination of Elderly PersonsReduction in Pneumonia and Influenza Hospitalizations and Deaths. JAMA. 1980;244(22):2547-2549. doi:10.1001/jama.1980.03310220045026