Search

Background: Despite vaccination, influenza commonly causes morbidity and mortality in institutional settings. Influenza control with rimantadine and amantadine is limited by emergence and transmission of drug-resistant influenza A variants, ineffectiveness against influenza B, and toxicity. This study evaluated the efficacy and tolerability of zanamivir versus rimantadine for influenza outbreak control in long-term care facilities. Methods: This double-blind, randomized, controlled study prospectively enrolled nursing home residents for 3 influenza seasons (1997 to 2000). Vaccine was offered to all subjects. Following influenza outbreak declaration, subjects were randomized to inhaled zanamivir 10 mg or standard of care (rimantadine 100 mg for influenza A or placebo for influenza B) once daily for 14 days. The proportion of randomized subjects developing symptomatic, laboratory-confirmed influenza during prophylaxis was the primary endpoint. Results: Of 482 randomizations (238 zanamivir, 231 rimantadine, 13 placebo), 96% of subjects were elderly or had high-risk conditions; over 90% were vaccinated. Symptomatic, laboratory-confirmed influenza occurred in 3% of zanamivir subjects and 8% of rimantadine subjects during chemoprophylaxis (P = .038; additional protective efficacy for zanamivir over rimantadine = 61%). Since only 25 subjects were randomized during 2 influenza B outbreaks and none developed influenza, the influenza B data were excluded from further analysis. Zanamivir was well tolerated and unassociated with emergence of resistant virus; rimantadine-resistant variants were common. Conclusions: This is the first prospective, controlled study demonstrating effectiveness of chemoprophylaxis for influenza outbreak control. Zanamivir prevents symptomatic, laboratory-confirmed influenza more effectively than rimantadine, is unassociated with resistant virus, and has a favorable safety profile. Zanamivir is an appropriate alternative for influenza outbreak control among institutionalized vaccinated elderly. [Copyright &y& Elsevier]

BACKGROUND. Large outbreaks of influenza A and B may occur in nursing homes despite high resident vaccination rates, even when the vaccine strain is matched to the circulating strain. This study reports the occurrence of separate influenza A and B outbreaks in a nursing home where more than 85% of residents were vaccinated. METHODS. Prospective surveillance was used to identify symptomatic residents in a rural Wisconsin nursing home with 680 residents. Viral cultures were obtained from all consenting residents identified with new respiratory symptoms even in the absence of temperature elevation. A "case" refers to a resident with a respiratory illness and an influenza isolate. RESULTS. During the 1992-93 season, 86% of 670 total residents were vaccinated, 104 (15.5%) were cases with influenza B. During the 1993-94 season, 89% of 690 total residents were vaccinated, 68 (9.8%) were cases with influenza A. The antigenic matches between vaccine and epidemic strains were characterized as "identical or minimal difference" by the Centers for Disease Control and Prevention. CONCLUSIONS. There is still a need to protect residents from infectious secretions and for contingency plans to permit the rapid use of antiviral agents. Future efforts are needed to develop vaccines that provide greater protection and to improve staff vaccination rates. [ABSTRACT FROM AUTHOR]