A new study suggests memory T cells might protect some people infected with SARS-CoV-2 by remembering past encounters with other human coronaviruses. The finding might help explain why some people seem to fend off COVID-19 and may be less susceptible to becoming severely ill. 

To come to this conclusion, researchers obtained and analyzed blood samples from 36 people who’d recently recovered from mild to severe COVID-19. All these individuals produced T cells that recognize multiple parts of SARS-CoV-2. They then compared this data to people who’d survived SARS. Interestingly, those memory T cells, acquired in response to SARS-CoV-1, also recognized parts of SARS-CoV-2. 

Finally, the team looked at healthy individuals with no history of either COVID-19 or SARS. To their surprise, more than half had T cells that recognize one or more of the SARS-CoV-2 proteins being studied. It’s still not clear if this acquired immunity stemmed from previous infection with coronaviruses that cause the common cold or perhaps from exposure to other as-yet unknown coronaviruses.

Overall, the study makes clear that past experiences with coronavirus infections may have something important to tell us about COVID-19. 

The findings, were recently reported in the journal Nature.

Additional information can be found in this blog post by NIH director Dr. Francis Collins.