Coronavirus outbreak largest study suggests elderly and sick are most at risk
The explanation for the generally heightened risk to the elderly, but also for the fact that Covid-19 kills many younger people even as some seniors survive, lies in a growing understanding of “immunosenescence.” Immunologists have identified some of the specific ways the immune system changes with age, allowing them to go beyond the simple assertion that it weakens.
“Older people are not as good at reacting to microorganisms they haven’t encountered before,” said physician and immunobiologist Janko Nikolich-Zugich of the University of Arizona College of Medicine. He calls it “the twilight of immunity.” [Source
Our immune systems have two sets of defenses against viruses and other pathogens: a first-line army of cells, called leukocytes, that attack invading microbes within minutes to hours, and a second-line force of precisely targeted antibodies and T cells that surge to the battle front as late as several days after.
It will, almost inevitably, be less successful in older people, because aged immune systems do not respond as well to immunisation.
It may be possible to overcome this by either giving multiple doses or giving it alongside a chemical (called an adjuvant) that gives the immune system a boost.