Striking decreases in the stress hormone cortisol were the strongest predictor for who develops long COVID-19 in new research that identified several potential drivers of the lingering symptoms afflicting millions of survivors.

Levels of cortisol in the blood of those with the post COVID-19 condition were roughly half those found in healthy, uninfected people or individuals who fully recovered from the pandemic disease, researchers at Yale School of Medicine in Connecticut and the Icahn School of Medicine at Mount Sinai in New York found.

No one knows yet what causes the constellation of symptoms, often termed long COVID-19, that afflict some 10% to 20% of people after the acute phase of infection with SARS-CoV-2, the virus that causes COVID-19. The U.S. government is spending more than $1 billion to learn why it occurs and devise strategies to treat and prevent the condition.