At risk of COVID-19
Then exercise at least 5 days per week

https://medicalxpress.com/news/2020-04-immune.html

Sample quote

"Exercise has anti-inflammatory benefits and promotes cellular repair, cell production and producing immune cells that help you fight off disease," he said.

In a study of 1,002 adults published in the British Journal of Sports Medicine in 2011, people who exercised at least five times a week cut their risk of colds by nearly half compared to people who were largely sedentary. Many of those who did get sick had less severe symptoms.

End quote