Covid-19 patients who are 80 or older are hundreds of times more likely to die than those under 40.

That’s partly because they are more likely to have underlying conditions — like diabetes and lung disease — that seem to make the body more vulnerable to Covid-19.

But some scientists suggest another likely, if underappreciated, driver of this increased risk: the aging immune system.

The changes that ripple through our network of immune cells as the decades pass are complex, resulting in an overreaction here, a delayed response there and over all, a strangely altered landscape of immunity.

Scientists who study the aging immune system say that understanding it may lead not only to a clearer sense of how age is connected to disease vulnerability, but to better strategies for vaccines and treatments for Covid-19.

As hope builds over possible frequent at-home testing, experts call the idea a long shot.

Over the past few weeks, a Harvard scientist has made headlines for a bold idea to curb the spread of the coronavirus: rolling out antigen tests, a decades-old underdog in testing technology, to tens of millions of Americans for near-daily, at-home use.