SARS-CoV-2, the virus that causes COVID-19, is a type of coronavirus, a family of viruses that also causes the common cold. Based on new findings, having a recent infection with the coronaviruses that cause the common cold and pneumonia, commonly referred to as endemic coronaviruses (eCoV), may reduce COVID-19 severity.

High levels of inflammation are common in the most severe cases of COVID-19. This inflammation can promote cytokine storm, an element of an overly aggressive immune response characterized by abnormally high blood concentrations of pro-inflammatory proteins called cytokines.

The investigators collected the electronic health records of patients who had received a comprehensive respiratory panel-polymerase chain reaction test (commonly known as PCR) between March 2015 and March 2020. This test is used to detect nucleic acids for eCoV and 16 other pathogens. Of the more than 15,000 participants included, 875 had a positive eCoV test, indicating they had experienced an active coronavirus infection within the previous five years.

Previous eCoV infection did not decrease the risk of SARS-CoV-2 infection; however, eCoV-positive patients demonstrated a statistically significantly lower risk of ICU admission and death upon hospitalization. People who had a previous eCoV infection were also less likely to require the use of a respirator.

This decrease in COVID-19 severity, but not SARS-CoV-2 infection rate in eCoV-positive patients, may be due to decreased cytokine storm injury. These results suggest immunological memory from a previous coronavirus infection does not impede viral replication and instead tempers the immune response.

The investigators caution that these results may not be generalizable, as the eCoV-positive people in this study were more sickly at baseline, participants were pooled from only one hospital location, and the study was observational in nature.

• Link to full study.