Where flu vaccination rates are higher in adults under 65, lower flu risk for seniors

September 10, 2015

Healthy adults who get the flu vaccine may help protect not only themselves but also older adults in their community at higher risk for serious complications from influenza, suggest findings from a new study published in Clinical Infectious Diseases. Based on a national sample of more than 3 million people across eight flu seasons, researchers observed that seniors were up to 21 percent less likely to be diagnosed with flu-related illness if they lived in areas where more adults under 65 were immunized.

In their observational study, the researchers looked at 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. In counties where at least 31 percent of the 18-to-64-year-old population was immunized against flu, elderly adults had a 21 percent lower chance of being diagnosed with a flu-related illness.

"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," Dr. Taksler said.

The reduction in risk for flu-related illness that the researchers observed was more than twice as large for seniors who were also vaccinated against flu themselves, compared to older adults who were not immunized, suggesting that communitywide vaccination may somehow boost the protection provided by individual vaccination. No direct association was observed between vaccine coverage among children and flu illness in the elderly, which suggests seniors may benefit most from the vaccination of other adults, with whom they are more likely to have direct contact.

As people age, their immune system weakens, which makes seniors more susceptible to flu. In recent years, between 80 and 90 percent of flu-related deaths and more than half of flu-related hospitalizations have occurred in people age 65 and older, according to the Centers for Disease Control and Prevention, which recommends that everyone 6 months of age and older get a flu vaccine every season.

The study's findings, which suggest but do not prove a cause-and-effect relationship between higher influenza vaccination rates among younger adults and fewer flu-related illnesses in seniors, may help inform vaccination policies and patient-physician discussions about the benefits of getting immunized against flu, the study authors noted. If confirmed by future research, the findings may have particular relevance in large metropolitan areas, where adults under 65 are often in contact with older adults, such as on crowded buses or subway trains, Dr. Taksler said.

Fast Facts

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Editor's note: The study authors' affiliations, acknowledgments, and disclosures of financial support and potential conflicts of interests, if any, are available in the article.

Clinical Infectious Diseases is a leading journal in the field of infectious disease with a broad international readership. The journal publishes articles on a variety of subjects of interest to practitioners and researchers. Topics range from clinical descriptions of infections, public health, microbiology, and immunology to the prevention of infection, the evaluation of current and novel treatments, and the promotion of optimal practices for diagnosis and treatment. The journal publishes original research, editorial commentaries, review articles, and practice guidelines and is among the most highly cited journals in the field of infectious diseases. Clinical Infectious Diseases is an official publication of the Infectious Diseases Society of America (IDSA). Based in Arlington, Va., IDSA is a professional society representing nearly 10,000 physicians and scientists who specialize in infectious diseases. For more information, visit http://www.idsociety.org. Follow IDSA on Facebook and Twitter.

Infectious Diseases Society of America

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