Aging immune systems aren’t as good at reacting to micro-organisms they haven’t encountered before.
COVID-19 kills an estimated 13.4% of patients 80 and older, compared to 1.25% of those in their 50s, and 0.3% of those in their 40s, according to a paper published on March 30 in The Lancet.
Studying data from China, British researchers from Imperial College London found that although 4% of patients in their 60s died from COVID-19, twice as many patients in their 70s—8.6%—did not survive the virus.
The chance that a COVID-19 patient would develop symptoms severe enough to require hospitalization also rose sharply with age. The rates of hospitalization were:
- 4% for patients 80 and older.
- 12% for patients in their 60s.
- 2% for patients in their 50s.
- 3% for patients in their 40s.
- 4% of patients in their 30s.
- 1% for patients in their 20s.
An analysis by STAT suggests several reasons behind the numbers.
Geriatrician and gerontologist George Kuchel of the University of Connecticut told writer Sharon Begley that having multiple chronic diseases and frailty could be more important than chronological age in determining a person’s response to COVID-19.
“An 80-year-old who is otherwise healthy and not frail might be more resilient in fighting off infection than a 60-year-old with many chronic conditions” because that 80-year-old may have a younger immune system.
As our immune systems age, they’re not as good at reacting to micro-organisms they haven’t encountered before, according to physician and immunobiologist Janko Nikolich-Zugich of the University of Arizona College of Medicine.
With advancing age, the body has fewer T cells, says Nikolich-Zugich. This leaves a depleted army of cells that can defend against a never-before-seen microbe. There’s also a communication problem between T cells and another set of cells that recognize invaders and instruct T cells to produce virus-killing compounds.
“The instructor cells grow scarce and start to do the biological equivalent of mumbling,” concludes Begley. “T cells therefore respond too late and too little.”