Flu shots may be especially important for older women who are socially active, a study from Japan suggests.

In a study of people over age 65, unvaccinated women who regularly participated in two or more social activities were twice as likely to report a flu infection as those who didn’t participate in any such activities, the study authors report.

At the same time, women who were vaccinated had no additional risk.

“It has been thought that vaccine effectiveness is relatively low in elder persons . . . but our research shows some meaning for older adults,” said lead study author Dr. Yugo Shobugawa of Niigata University in Niigata, Japan.

Worldwide, the flu affects 3-5 million people annually and can result in 300,000 to 650,000 deaths, according to the World Health Organization. In industrialized countries, most of these deaths occur among adults over age 65 who develop secondary infections such as pneumonia.

“Effectiveness of the influenza vaccine varies by season because circulating strains vary and are gradually evolving,” Shobugawa told Reuters Health by email. “However, this suggests a need for further efforts to promote vaccination, particularly among socially active elders.”

Shobugawa and colleagues analyzed data for more than 12,200 men and 14,000 women over age 65. They examined the association between flu infection and social participation in volunteer groups, sports groups, leisure activity groups, senior citizen clubs, neighborhood associations, cultural groups, nursing care or health promotion groups, local events and grandchild-rearing support.

Among men, social participation wasn’t associated with developing the flu, and it didn’t vary among vaccinated or unvaccinated men.

Respiratory disease, however, nearly doubled a man’s chance of getting the flu, regardless of whether he was vaccinated or unvaccinated.

Vaccines may help reduce the spread of infection among social groups, the study authors wrote in the journal BMJ Open, and when no vaccine is available, non-pharmaceutical precautions such as respiratory hygiene and cough etiquette could help as well.

Although social participation increases social contact and the risk of flu infection, that doesn’t mean older adults should stop participating in their social activities, they added.

“Social participation has been linked to healthy aging and the maintenance of functional independence in older individuals,” said Dr. Yukinobu Ichida of the Doctoral Institute for Evidence Based Policy in Tokyo, Japan. Ichida, who wasn’t involved with this study, has researched social participation and self-rated health among older adults in Japan.

“Our findings suggest that participation in the community improves self-rated health,” Ichida said. “Investing in that community infrastructure to boost social participation may help promote healthy aging.”