ABSTRACT
BACKGROUND: Significant morbidity and mortality may result after influenza infection in the elderly. Influenza vaccination is recommended for all persons older than 65 years but does not confer universal protection against disease or complications. Chemoprophylaxis against influenza with oseltamivir is effective in a younger unvaccinated population but has not been studied in an elderly vaccinated population.
POPULATION STUDIED: The study population included residents of long-term care facilities located throughout the United States and Europe. Of the 548 subjects enrolled (272 placebo, 276 oseltamivir), 493 completed the study. Study groups were similar at baseline. Residents 65 years and older were included; the mean age was approximately 81 years. Participants had a mean of 6.1 concurrent diseases and were taking an average of 7.7 medications. Approximately 80% of participants received the influenza vaccination.
STUDY DESIGN AND VALIDITY: This was a randomized double-blind placebo-controlled study. Participants were recruited during the 1998-1999 influenza season and performed a stratified randomization according to vaccination status and coexistence of chronic obstructive airways disease. Subjects took either oseltamivir 75 mg or placebo once daily for 6 weeks. Treatment was started when influenza infection was detected in either one resident of the center or in two individuals in the immediate community. Participants were examined at 3, 6, and 8 weeks and when influenza-like symptoms were documented on daily diary cards.
OUTCOMES MEASURED: The primary outcome was incidence of laboratory-confirmed clinical influenza A or B, defined as fever, one respiratory symptom, and one constitutional symptom plus a greater than 4-fold increase in influenza antibody titer or viral replication from nasal or throat swabs. Secondary outcomes included symptomatic laboratory-confirmed influenza not meeting clinical criteria, asymptomatic laboratory-confirmed influenza, influenza-like illness, and secondary influenza complications (otitis media, sinusitis, bronchitis, or pneumonia).
RESULTS: Thirteen cases of laboratory-confirmed clinical influenza were identified; 12 of the 13 infected patients previously had been vaccinated. No influenza occurred in 22 of the 31 participating study sites. Compared with placebo, treatment with oseltamivir significantly protected against laboratory-confirmed influenza (4.4% vs. 0.4%; P=.002; number needed to treat [NNT]=25) and reduced secondary influenza complications (2.6% vs 0.4%; P=.037; NNT=45). The difference in rates of pneumonia (1.1% vs 0.0%) is not clinically significant. Adverse events were not more likely in oseltamivir-treated patients and withdrawals due to adverse events was similar among the patients in the 2 groups. One patient died in each study group (unrelated to influenza or study medication).
In this study of frail elderly residents of nursing homes, most of whom had been vaccinated, the addition of oseltamivir (Tamiflu) prophylaxis produced a reduction in episodes of influenza during the 1998-1999 season. The impact was small — one additional episode of influenza was prevented for each 25 patients treated. At a cost of $270 per person for 6 weeks of therapy, which works out to $6750 to avoid one additional case of influenza and $12,150 to prevent one additional complication, the benefits of the addition of oseltamivir to previously vaccinated persons may not be worth the cost.