SARS-CoV-2, the virus that causes COVID-19, is one of the coronaviruses, a large family of viruses that typically causes mild to moderate upper-respiratory tract illnesses, like the common cold. Findings from a new study demonstrate that exposure to common cold coronaviruses may provide immunity to SARS-CoV-2.

The average person has one or two episodes of the common cold every year. The immune system responds to cold-causing viruses by producing B cells. These cells make antibodies, which in turn neutralize the viruses, rendering them harmless. Some B cells become memory B cells, which can remain in the body for a long time, even after the virus is cleared, to efficiently recognize and destroy returning viruses.

The authors of the study analyzed blood serum and peripheral blood mononuclear cells (a type of immune cell) from 21 healthy people who had never been exposed to SARS-CoV-2 (sampled before the emergence of the virus) and 26 people who were recovering from COVID-19 (sampled four to nine weeks after showing symptoms). In particular, they looked for reactivity against two proteins – the S and N proteins – of SARS-CoV-2 and the S proteins of two coronaviruses that cause colds in people. The S, or spike, proteins are shared characteristics of all coronaviruses.

They found that the memory B cells that formed following common cold exposure did not differentiate between the different coronaviruses, but instead showed cross-reactivity to the S protein on the SARS-CoV-2 virus to elicit immunity. These findings indicate that having a common cold might provide some degree of protection against SARS-CoV-2, but they do not demonstrate the extent or duration of protection conferred.

• Link to full study.