A new study reveals that even the sickest COVID-19 patients produce T cells to fight the virus. Researchers from La Jolla Institute for Immunology tracked 10 COVID-19 patients with severe symptoms and found that they all produced T cells targeting SARS-CoV-2, the virus that causes COVID-19.

T cells are known as the immune warriors that help us fight viruses. The new study shows that people have these warriors in their system that can target the virus and may help them recover, according to an article published in Science.

“This is encouraging data,” said virologist Angela Rasmussen, of Columbia University, who says it “bodes well for the development of long-term protective immunity” and could help researchers develop better vaccines.

Currently the more than 100 vaccines in development are focusing on antibodies, which offer another immune response. T cells act differently. Instead of preventing the virus from attaching to human cells like protein antibodies, they spur the body’s immune response into action not only to deploy antibodies, but also to send “killer” T cells into battle to target and destroy infected cells, according to Science.

According to Fox News, the new study means that an effective vaccine will have to include T cells to work with antibodies.

“This is key to understanding how the immune system works,” said Alessandro Sette, a professor at La Jolla Institute for Immunology, and a co-author of the study. “You want vaccine approaches to be grounded in observations from rather diverse settings to ensure that the results are generally applicable.”

The researchers said it was clear that T cells worked hand-in-hand with antibodies to target SARS-CoV-2 to try and halt infections.

“Activating these cells appears to be at least as important as the production of antibodies,” said virologist Rory de Vries, who co-led the study, according to Fox News.