There is no doubt that your immunity weakens with age. At no time was that more obvious than during the COVID-19 pandemic. People over 65, particularly those in nursing homes or in densely populated areas, succumbed quickly to the virus and were much more likely to die when infected than any other category of people.

That’s because when we get old, we have increased susceptibility to infectious diseases and a decreased response to vaccination, as your immune system might be a bit crotchety and unable to respond robustly to the boost. This decline is called immune system senescence or immunosenescence—the process of gradual deterioration of the immune system because of age.

Immunosenescence has a major effect on your innate and adaptive immune response. When your thymus disappears after puberty, the output of naïve T lymphocytes and antigen experienced T cells accumulate. The T cell repertoire is fixed as highly differentiated effector T cells, and they produce more proinflammatory cytokines, which together with activated innate cells contribute to a systemic inflammatory climate in older age.

In other words, the cells — just like you — are getting older, and they might not be as up to their game as they were when you were 25, which is why there tends to be more inflammation with age.

This edgy profile is just like the situation in the blood of women after giving birth; it is the body’s way of maintaining some stability.

Immunosenescence usually coincides with the waning of your levels of sex steroid hormones, the decrease in healthy organisms in your biome, and the worsening of comorbidities such as diabetes, dementia, and congestive heart failure, in addition to an overall decrease in the ability of your kidneys to clear toxins from the blood.

Notice that I said “usually.” Because every person is different, every person experiences this senescence differently and to different degrees.

You might respond well to vaccines (as many did to the COVID-19 versions), be relatively free of comorbidities, and/or maintain your sex drive, libido, and biomes as you approach 100. Some of the variation depends on immunogenetics — the genetics of your immune system. These genetics play a major role in how your immune system stays healthy as you age, particularly when it comes to your biological sex and the hormones you produce