People with severe cases of COVID-19 may produce more T cells to protect against reinfection, according to a new study.

Researchers at La Jolla Institute for Immunology, The University of Liverpool, and the University of Southampton found that the harder hit by the virus, the more people’s immune systems reacted to the pathogen by sending out T cells that provided long lasting protection. Some of the study subjects were so ill, they needed to be hospitalized, but these were the people that generated the highest number of the warrior T cells.

Dr. Christian Ottensmeier, professor of Immuno-Oncology at the University of Liverpool, called T cells “the guys with the guns in the army who eliminate the threat,” according to NBC San Diego. He added that he hoped the T cells would remain active “for many months. Perhaps a year, maybe longer than that.” He said researchers would continue to monitor the study participants to determine how long the protection lasts.

A study published in the BMJ last November found that T cell immunity lasted for at least six months even after mild or asymptomatic cases of COVID-19. Researchers also found a correlation between the intensity of T cells during their peak disease-fighting activity and the duration of their protection against the virus. Experts believe that the strong T cell response that COVID-19 patients produce after becoming infected with the virus bodes well for long-term immunity produced by the vaccines.