Bill Fisher blasted off Earth in 1985 aboard a NASA space shuttle, speeding 18,000 mph through the atmosphere.

Fisher, now a 74-year-old emergency room physician, tweeted Wednesday: "I am genuinely more concerned about going to work tomorrow morning than I was the day I launched on the space shuttle.".

That's because the coronavirus (which causes the respiratory disease COVID-19) is easily spread, can be excruciating, and is most deadly in people over 60.

Fisher wrote that he had a 1.5 percent chance of dying on a space shuttle, which flew 135 missions over 30 years.

I am genuinely more concerned about going to work tomorrow morning than I was the day I launched on the space shuttle.

1.5% shuttle mortality vs 9-12% if I get COVID-19.

Meanwhile, a new study released on March 30 in the journal The Lancet Infectious Diseases found that the overall fatality rate from COVID-19 is 0.66 percent — making it over six times more lethal than the flu.

Previously, Anthony Fauci, the well-regarded director of the National Institute of Allergy and Infectious Diseases, estimated that overall COVID-19 is 10 times more lethal than the flu.

(Flu deaths in the U.S. are dominated by the elderly, with 70 to 85 percent of deaths occurring in people 65 and older).

The pronounced mortality numbers for older people (Americans aged 20–54 years have a mortality of less than 1 percent) is a critical reason why infectious disease experts implore younger folks to social distance.