Women's immunity to flu vaccination decreases with age

Generally women have a greater immune response to flu vaccinations as compared to men. However, their immunity weakens as they age and their estrogen decline, suggests a study.

The study was published in the journal of 'npj Vaccines'.

"We need to consider tailoring vaccine formulations and dosages based on the sex of the vaccine recipient as well as their age," said Sabra Klein, the study's senior author.

First, the researchers evaluated immune responses to the 2009 H1N1 influenza vaccine among 145 human volunteers -- one group age 18-45 years, the other of 65 and the olders.

Analysing key markers of the immune response, the researchers found that, on average, women in the younger group had a stronger response as compared to both the men and the older women.

The younger women had, for example, a jump in their levels of the important immune protein -- IL-6 -- that was almost three times greater than that seen in the younger men, and almost double seen in the older women.

Measures of the anti-flu antibody response also were higher for the younger women as compared to the men and the older women, though the greatest differences were between the younger and the older women.

The team conducted a similar set of experiments in adult and aged mice and observed similar results.

In the mice and in the human volunteers, the younger females, as expected, had higher bloodstream levels of estradiol, one of the important estrogens, as compared to the older, post-menopausal females.

Similarly, the younger males had higher bloodstream levels of testosterone compared to older males. Stronger vaccine response was linked to higher estradiol among the females and, more weakly, to lower testosterone among the younger males.

Klein and her colleagues found evidence that this association with sex hormone levels was causal.

"What we show here is that the decline in estrogen that occurs with menopause impacts women's immunity," said Klein.

"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," Klein added.