September 30, 2015
High Influenza Immunization Rates Among Younger Adults Help Protect Elderly

Cleveland—Pharmacists who persuade younger adults to get influenza vaccinations are not just helping them avoid an extremely unpleasant illness, they also are protecting the elderly, who are much more likely to require hospitalization or even die from the flu.

That’s according to a new study published in Clinical Infectious Diseases. Cleveland Clinic researchers, who used a national sample of more than 3 million people across eight flu seasons, found that the elderly were as much as 21% percent less likely to be diagnosed with flu-related illness if they lived in U.S. counties where at least 31% of adults under 65 were immunized.

For the observational study, the study team focused on the association between countywide flu vaccination rates for adults age 18 to 64 and illnesses related to influenza among 3.3 million Medicare beneficiaries 65 and older between 2002 and 2010.

“Our findings suggest that flu vaccination should be encouraged among low risk adults not just for their own benefit, but also for the benefit of higher risk adults in their community, such as the elderly,” said study author Glen B. Taksler, PhD, of the Cleveland Clinic. “In round numbers, we estimated that about one in 20 cases of influenza-related illness in the elderly could have been prevented if more non-elderly adults had received the flu vaccine.”

Compared with older residents of counties with fewer than 15% of younger adults vaccinated against the flu, the adjusted odds ratio for a principal diagnosis of influenza among elderly residents was 0.91 for counties with 16% to 20% of younger adults vaccinated; 0.87 for counties with 21% to 25% vaccinated; 0.80 for counties with 26% to 30% vaccinated, and 0.79 for counties with 31% or greater vaccinated, according to the results.

When the older adults also were vaccinated against the flu in areas with higher immunization rates, their reduction in risk more than doubled compared to those who were not immunized. Study authors said that seems to suggest that communitywide vaccination somehow boosts the protection provided by individual vaccination.

Other strong associations for risk reduction were observed in peak months of influenza season, in more severe influenza seasons, in influenza seasons with greater antigenic match to influenza vaccine, and for more specific definitions of influenza-related illness.

Interestingly, the study identified no direct association between vaccine coverage among children and flu illness in the elderly. Instead, seniors benefitted the most from the vaccination of other adults, possibly because they were more likely to have more direct contact with them, the researchers posit.

Background information in the article notes that, in recent years, between 80% and 90% percent of flu-related deaths and more than half of flu-related hospitalizations have occurred in patients 65 and older.

Taksler pointed out that, if confirmed by future research, the findings could be especially beneficial in large metropolitan areas, where adults under 65 are often in contact with older adults, such as on crowded buses or subway trains.

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