Here's some bad news for older women during flu season: Aging reduces the stronger immune response that women typically have to vaccination, a new study finds.
"We need to consider tailoring vaccine formulations and dosages based on the sex of the vaccine recipient, as well as their age," said study senior author Sabra Klein. She is an associate professor in the department of molecular microbiology and immunology at Johns Hopkins Bloomberg School of Public Health in Baltimore.
It was already known that women typically have stronger immune responses to vaccines than men, and that older people tend to have weaker responses than younger folks. In this study, the researchers wanted to learn more about the interaction of these sex- and age-related differences.
Klein and her colleagues assessed immune responses to the 2009 H1N1 flu vaccine in two groups: 50 adults aged 18 to 45, and 95 adults aged 65 and older.
Women in the younger group had a stronger immune response than older women and all men.
For example, increases in levels of the important immune protein IL-6 in younger women were nearly three times greater than in younger men, and almost twice that in older women.
Experiments with mice yielded similar findings.
Overall, the findings suggest that estrogen boosts women's immune response to flu vaccines and testosterone lowers men's immune responses to the vaccines. However, women's responses grow weaker as their estrogen levels decline with age.
The findings likely apply to other vaccines, according to the Johns Hopkins researchers.
"What we show here is that the decline in estrogen that occurs with menopause impacts women's immunity," Klein said in a Hopkins news release. "Until now, this hasn't been considered in the context of a vaccine. These findings suggest that for vaccines, one size doesn't fit all -- perhaps men should get larger doses, for example."
The study was published recently in the journal npj Vaccines. The team is now investigating how estrogen boosts the immune system's response to vaccines.