Sequential outbreak of influenza A and B in a nursing home: Efficacy of vaccine and amantadine

OBJECTIVE: To describe the sequential occurrence of influenza A and B in a nursing home, and to determine the efficacy of influenza vaccine and/or amantadine treatment with respect to incidence and sequelae. SETTING: The Jewish Home and Hospital for Aged, a skilled-care nursing facility. PARTICIPANTS: Of 499 frail older nursing home residents, 139 contracted influenza during the study period (mean age 87.5 years; SD = 6.7). The residents were followed from February through April 1988. INTERVENTION: Influenza vaccine and/or amantadine. MEASUREMENTS: Episodes of influenza and their sequelae, i.e., pneumonia, hospitalization, and death. RESULTS: The vaccine had no effect on the incidence of influenza-like illness, length of illness, or the associated death rate. It reduced the rate of pneumonia secondary to influenza A and B (relative risk = .57; 95% CI: .37 to .89; P = .023). Amantadine did not affect the attack rate of influenza nor the rate of pneumonia secondary to influenza. It was associated with decreased mortality (relative risk = 0; P = .001), and shorter length of influenza A illness (P(Wilcoxon) = .082). Although the combination of amantadine and vaccine did not affect length of influenza (A or B) illness, it was associated with a significantly lower rate of sequelae (relative risk = .58; 95% CI: .36 to .95; P = .024). CONCLUSION: In this epidemic, the combination of amantadine and vaccine was most effective in reducing the rate of influenza-associated sequelae. The possibility of a 'biphasic' epidemic prompts consideration of vaccinating nonimmunized nursing home residents, even though it may be late in the influenza season.