[Impact of influenza epidemics and efficacy of vaccination among geriatric inpatients].

To determine the impact of influenza epidemics among geriatric inpatients and to monitor the clinical efficacy of influenza vaccination, the influenza infection rate in non-vaccinated inpatients was determined serologically and the incidence of febrile episodes and death were compared between the vaccinees and non-vaccinees hospitalized in the referred hospital from January through September, 1995. Three influenza subtypes, influenza A/H1N1, A/H3N2, and B, were endemic simultaneously from January to March in 1995. The pattern of incidence of febrile episodes varied for each ward. A total of 123 non-vaccinated inpatients were tested for elevation of serum hemagglutination inhibition titer to the three subtypes of influenza virus. Of these, 58 (47.2%) patients were infected with at least one of the influenza viruses during the epidemic of 1995. No patient with pre-existing HI titer over 128X was infected with any of three types of influenza, indicating that HI titer over 128X is the protective level. The febrile episode frequency was significantly higher in the non-vaccinees than in the vaccinees (49.6% vs. 32.6%), but it was quite comparable in the two groups after the influenza epidemic (34.9% vs. 35.8%). The number of observed deaths from January to September of 1995 was 4 (4.9%) in the vaccinee group and 12 (9.8%) in the non-vaccinee group. These results suggest that influenza epidemics have a striking impact on geriatric inpatients and that influenza vaccination has significant efficacy for the reduction of harmful events associated with influenza infection.