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

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

1. 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, who are more susceptible to flu due to a weakening of the immune system as people age.

2. In this observational study, in counties where at least 31 percent of adults age 18 to 64 were immunized against flu, elderly adults had a 21 percent lower chance of being diagnosed with an illness related to flu.

3. The reduction in risk for flu-related illness was more than twice as large for older adults 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.