In an article discussing whether to excercise while ill (generally not; it won’t help, will infect others, and sometimes make you worse, the article advises, but says Mayo Clinic says it’s ok to expose your gym to a head cold—let’s hope there’s no one there with leukemia or on anti rejection medication),
Abstract of article is here
https://www.tandfonline.com/doi/abs/10.1080/15438629609512057
One study from the 1990s published in the journal Sports Medicine, Training and Rehabilitation found evidence suggesting exercising with the flu could noticeably increase your odds of developing a type of chronic fatigue syndrome that could last for years.
Abstract of article is here
https://www.tandfonline.com/doi/abs/10.1080/15438629609512057