It is reasonable to hypothesize that Women might have evolved a particularly fast and strong Immune response in order to protect developing fetuses and newborn babies. Hormones play an important role to boost the immune response. Oestrogen can activate lymphocytes and dendritic cells in the antiviral response, while testosterone tend to suppress the inflammatory response.

Genetic factors may also explain the sex-related difference in the immune system. Encoded by a gene on the X chromosome, TLR7, which detects viruses and activates immune cells, causes a stronger immune response in women than in men. A Strong Immune Response is evolutionary advantageous for women, but in some cases it may become injurious. Indeed, women are more prone than men to develop autoimmune diseases such as multiple sclerosis and lupus. In the case of vaccines, they suppress the production of an anti-inflammatory protein in girls, but not boys. This boosted the girls’ immune responses, and may have made the vaccine more effective. The difference between sexes is really significant and it may be associated to different responses to disease and medication. However, the NIH does not track whether investigators in the clinical trial have actually evaluated any differences between them.