This phenomenon, known as immunosenescence, may explain why older age groups have been particularly hard hit by COVID-19. And there’s another troubling implication: vaccines, which “incite” the immune system to fight off “invaders,” often perform poorly in the elderly. The best strategies for coping with a pandemic may fail to pinpoint the groups that need it most.
Scientists have known for decades that an aging immune system can expose the body to infection and weaken their response to vaccines. In June, the US Food and Drug Administration announced a COVID-19 vaccine must protect at least half of vaccinated individuals to be considered effective. But protection in older adults may not meet that standard.
“No vaccine is as effective in the elderly as it is in young people,” said Matt Kaeberlein, a gerontologist at the University of Washington, Seattle.
The human immune system is very complex and aging affects nearly every component. Some types of immune cells become depleted. For example, older adults have fewer naive T cells that respond to new invaders, and fewer B cells, which produce antibodies that attach to invading pathogens and target them for destruction.
The Nature.com page also mentions that older people tend to experience low-grade chronic inflammation, a phenomenon known as inflammation (see graphic). Although some inflammation is a key part of a healthy immune response, this constant buzz of internal activation makes the immune system less responsive to external attacks.
“It is this pervasive, chronic inflammatory condition that drives most of the immune dysfunction we see,” says Kaeberlein. The result is a worse reaction to infection and a blunted response to vaccines, which work by deploying the immune system to fight pathogens without actually causing disease.
With about 50 COVID-19 vaccine candidates currently being tested in humans, the researchers say, it is not clear how this will affect older adults. In a phase I study of 40 people aged 56 and over, Moderna in Cambridge, Massachusetts, reported that the mRNA-1273 candidate gave rise to the same antibody levels as those in younger age groups.
Biotechnology China Sinovac in Beijing, which tested a candidate for CoronaVac in a phase I / II study involving 421 adults aged between 60 and 89 years, announced in a press release on Sept. 9 that it appears to be working in older adults too – it happened to those who younger.