When Young Adults Get Flu Shots, Older Adults Benefit Best

Low-risk adults help prevent disease in higher-risk populations

Your annual flu shot does more than keep you from coming down with the virus. It also may protect the older adults around you from getting the bug — people who are at higher risk of developing serious complications from the illness, a new study says.

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The study, published recently in the journal Clinical Infectious Diseases, suggests a link between the flu immunization rates of young adults and lower flu risk for older adults.

In their observational study, the researchers looked at countywide flu vaccination rates for adults ages 18 to 64 and then compared them to influenza-related illnesses among 3.3 million Medicare beneficiaries 65 and older. Data were from the years 2002 to 2010.

In counties where at least 31 percent of adults between ages 19 and 64 had the flu vaccine,  adults older than age 65 had a 21 percent lower chance of being diagnosed with a flu-related illness.

“This indicates that older adults were less likely to be diagnosed with the flu if they lived in communities where younger, healthy adults received the flu vaccine,” says the study’s author Glen Taksler, PhD, a researcher in Cleveland Clinic’s Medicine Institute.

Young, healthy adults are unlikely to develop serious complications from the flu — although some flu seasons, such as 2009-2010, were particularly severe for younger age groups.

But young adults may spread disease to other people in the community who are at much higher risk of hospitalizations and other serious complications from influenza, such as older adults or those with weakened immune systems.

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Boosting community immunity

You may have heard of the term herd immunity or community immunity. This occurs when a critical portion of a community is immunized against a contagious disease. The result is most members of the community are protected against that disease because there is little opportunity for an outbreak.

You’re building herd immunity when you get a flu shot, because you’re less likely to spread germs to other people with whom you come in contact. The end result is you’re preventing disease in people who might ultimately get sicker than you would.

A yearly flu vaccine is recommended for all adults and children older than 6 months, but the vaccine is less effective for older adults than it is for younger people.

As people age, their immune system weakens, which makes older adults more susceptible to flu. More than half of flu-related hospitalizations and 80 percent to 90 percent of flu-related deaths occur in people age 65 and older, according to the Centers for Disease Control and Prevention.

The researchers observed that the risk reduction for flu-related illness was more than twice as large for seniors who received the flu vaccine, compared to older adults who were not immunized. This may suggest that community-wide vaccination somehow boosts the protection provided by individual vaccination, Dr. Taksler says.

“An older adult may be doing everything possible to prevent catching the flu. But they may be able to get an extra benefit from other people in the community who are vaccinated,”  Dr. Taksler says.

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Extra effort

The study suggests that adults who have contact with the elderly should make a particular effort to get the flu vaccine, Dr. Taksler says.

This includes people with older adults in their household, and those who have contact with them in the community – such as at work, on a crowded bus or in other public places.

“We estimated that about one in 20 cases of influenza-related illness in older adults could have been prevented if more of the younger adults had received the flu vaccine,” Dr. Taksler says.

If confirmed by future research, the findings may have the most significance in large metropolitan areas, where adults younger than age 65  often are in contact with older adults, Dr. Taksler says.

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