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Why is COVID-19 so deadly to elders?

Lisa M. Krieger, The Mercury News on

Published in Health & Fitness

SAN JOSE, Calif. -- Today, like every day, Eric Verdin will cycle the steep hills of Marin County. He'll wait until noon to eat his first meal. He'll wear a mask and stay socially distanced. He'll be asleep no later than 11 p.m.

Despite his excellent health, the 63-year-old scientist and CEO of the Buck Institute for Research on Aging knows he must do everything he can to protect himself from this hard truth: As we age, our body's elegant symphony of immune cells turns dissonant. We may feel fine. But our hidden defenses no longer fully shield us -- and may turn against us.

As COVID-19's case count explodes, "This is the time more than ever to adopt the healthiest lifestyle that you can," he said. "Sleep, nutrition and exercise is the trifecta that will position you to respond to the virus in the best way possible. You'll be in better condition to resist."

When we're young, our bodies develop a well-tuned network of protection against foreign invaders like the COVID-19 virus. It's a two-tiered system. The first line of defense, the so-called innate response, acts like the Border Patrol, promptly attacking any invader. It's a generalist, trained to take on all comers, and makes up in speed what it lacks in specificity. The second line of defense, the adaptive response, acts more like our military -- slower to respond, but skilled in its precision. When we get older, both systems fail -- in different ways. "It's a double whammy," said Verdin.

The adaptive response weakens, so is less able to fight off infection. That's because our thymus, which produces infection-fighting T cells, reaches its peak size at puberty and then steadily shrinks. There's a decline in the number, activity and diversity of T cells, a process scientists dub "immunosenescence." By the age of 50, our T cell production is less than 10% of its peak.

"We live on our reserves," said Dr. Cornelia Weyand, director of the Center for Translational Medicine and professor of medicine at Stanford University School of Medicine.

 

The infection surges and spreads to more organs, causing greater illness. And it's harder for an older person to clear the virus from the blood.

To make matters worse, there's emerging evidence that this new virus actually kills immune cells, either directly or indirectly. One of the key predictors of poor outcome in the ICU is when a patient develops what's called lymphopenia -- a dangerously low level of infection-fighting lymphocytes in the blood -- between four and six days after disease onset.

The innate response has the opposite problem: as it ages, it gets cranky and aggressive, causing chronic inflammation in the lungs and other organs. Elders live with a smoldering low-grade inflammation that is so common scientists have a name for it: "inflamm-aging."

When attacked, "it becomes overactive. It goes crazy," said Verdin, who leads the Novato-based institute, the first independent biomedical research facility in the world focused solely on aging. Infection by the COVID-19 virus triggers a rush of immune cells into the lungs, causing patients to suffocate.

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