Research published today in Cell Reports Medicine reveals key biological differences that may explain why women with long COVID — especially those who develop chronic fatigue syndrome — tend to experience more severe and persistent symptoms than men do.

Post COVID-19 condition, or long COVID, is diagnosed when neurological, respiratory or gastrointestinal symptoms develop or continue three months or more after an acute SARS-CoV-2 infection.

The likelihood of developing long COVID is three times higher for women than men, but until now the underlying biological mechanisms driving this disparity have remained unknown.

The new research suggests potential targets for treatment that could bring relief to the 3.5 million Canadians who reported having had long COVID as of June 2023, according to Statistics Canada.

“We are focusing on a subset of patients with the most devastating symptoms that are very similar to chronic fatigue syndrome,” explains principal investigator Shokrollah Elahi, an immunology professor in the Mike Petryk School of Dentistry. “They didn’t have these symptoms prior to COVID and most had only mild COVID-19 disease, so they were not hospitalized.”

Elahi’s team carried out blood and genetic tests on 78 patients with long COVID one year after their acute diagnosis, as well as a control group of 62 people who did not develop long COVID after infection with SARS-CoV-2.

Through analysis of immune cells, biomarkers in the blood and RNA sequencing, they identified a distinct immune signature in female versus male patients.