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

Abstract

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 (PWilcoxon = .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.