Emergency wards remain busy two years after the first COVID-19 vaccines arrived in Ontario in part because the virus depletes the body’s supply of T-cells, leaving young and old alike vulnerable to secondary infections, says a University of Waterloo immunologist.

T-cells are the front-line soldiers of the immune system, and the number of T-cells typically increases when the body is fighting off an infection, said Barb Katzenback, who studies viruses.

“Individuals who are infected with COVID have many fewer T-cells,” said Katzenback. “That’s a problem for us because T-cells are a really important part of our immune system that helps defend us against infection.”