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Long-Term Effectiveness of Flu Vaccine in Community-Dwelling Elderly Persons

A 10-year multicenter study shows that influenza vaccination reduces rates of hospitalization and death in elderly persons.

Although yearly influenza vaccination is recommended in the U.S. for elderly persons, only about 60% of this population is vaccinated — well short of the 90% goal. Estimates of influenza-vaccine effectiveness in the elderly are based mostly on short-term studies covering one or two influenza seasons at a single site.

To address issues of seasonal and geographic variability, as well as potential bias and residual confounding, investigators conducted a large-scale, multicenter, long-term study of vaccine effectiveness in community-dwelling individuals aged 65. Data concerning influenza vaccination status were pooled from three HMOs (one in Minnesota/Wisconsin for 1990–1991 through 1999–2000, and one each in Oregon/Washington and New York for 1996–1997 through 1999–2000), totaling 713,872 person-seasons of observation.

Compared with nonvaccinees, vaccinees had a 27% reduction in hospitalization for pneumonia or influenza and a 48% reduction in death from any cause. Significant benefits were observed across age and risk subgroups. Statistical modeling analysis of a hypothetical undetected confounder that might have influenced vaccine effectiveness reduced but did not eliminate the observed vaccination benefits.

Comment: This 10-year, geographically diverse, multicenter study counters concerns that previous findings of vaccine effectiveness might have been influenced by characteristics unique to a single influenza season or a localized study population. Still, as an editorialist notes, current vaccines are less immunogenic and probably less effective in the elderly than in younger, healthy adults. Thus, more-protective vaccines are needed for the elderly. Also, enhanced influenza vaccination programs among children may interrupt virus transmission and provide secondary protection to elderly persons, as has occurred with pneumococcal vaccines.

— Neil R. Blacklow, MD

Published in Journal Watch Infectious Diseases October 3, 2007

Citation(s):

Nichol KL et al. Effectiveness of influenza vaccine in the community-dwelling elderly. N Engl J Med 2007 Oct 4; 357:1373.

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• Medline abstract (Free)

Treanor JD. Influenza — the goal of control. N Engl J Med 2007 Oct 4; 357:1439.

• Original article (Subscription may be required)
• Medline abstract (Free)