September 16, 2015
Nursing Home Study Proves Benefit of Influenza
Vaccine in Elderly
Providence, RI—How effective influenza vaccine is in reducing deaths and hospitalizations in the elderly appears to come down to the answer to one question: Is it well matched to that season’s circulating viruses?
That’s according to a new study published recently in the Journal of the American Geriatrics Society. Brown University researchers analyzed the medical records of millions of nursing home residents, finding that, between 2000 and 2009, the better match the vaccine was to prevalent flu strains, the fewer nursing home residents died or were hospitalized.
Influenza vaccination is a standard of care and a measure of quality in nursing homes, yet some public health experts question the evidence for its benefit, explained corresponding author Vincent Mor, PhD, of the Brown University School of Public Health. Proving effectiveness can be difficult, however, because clinical trials that would withhold vaccination for a control group are not ethical, and observational studies that track differences among those who are vaccinated and those who are not might not take all factors into account, Mor added in a Brown press release.
If influenza vaccine is overall ineffective for the elderly, the researchers posited, then no benefit would be detected when the formula was a better match as compared to a poor match. The study took advantage of the natural variation over the decade 2000 to 2009 to see whether nursing home residents had fewer deaths and hospitalizations when the match was good.
“What we've used is the randomness of the match,” Mor said. “Ours is the first study to, we think, come up with an unbiased approach.”
The results found that the match rate varied a large amount in the flu strain A/H3N2, which leads to most flu hospitalizations and deaths. Over the 10-year study period, the match rate ranged from 11.2% in 2003-2004 and 22% the next year, to 100% in the first two study years and in the last one. Meanwhile, match rates for strain A/H1N1 were usually very high but tended to be low for B strains.
Comparing weekly deaths and flu-related hospitalizations in each year's flu season, the researchers calculated that, for every percentage point increase in the A/H3N2 match rate, weekly deaths declined by about 0.0016 and hospitalizations declined by about 0.002 per 1,000 nursing home residents.
While the numbers appear small, a 50-percentage point increase in the match rate for a flu season would save the lives of 2,560 people and prevent 3,200 hospitalizations among 1 million elderly nursing home residents, the results showed.
“This study evidences protection for an elderly population for whom vaccine efficacy has been questioned,” said co-author Stefan Gravenstein, MD, MPH, adjunct professor of medicine and health services, policy and practice. “Annual vaccination is the only way to maximize the benefit of vaccine, no matter what the age.”
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