People exposed to harmless coronaviruses have more immunity to SARS-CoV-2

People exposed to harmless coronaviruses have more immunity to SARS-CoV-2

Population immunity to SARS-CoV-2 can be obtained after contracting COVID-19 or through vaccination. This immunity is considered crucial for overcoming the COVID-19 pandemic.

Now, a team of researchers, led by the University of Zurich, has discovered another component that contributes to immunity to SARS-CoV-2. Alexandra Trkola, head of the University’s Institute of Medical Virology, said: “People who have strong immune responses to other human coronaviruses also have some protection against SARS-CoV-2 infection.”

The researchers analyzed antibody levels against four other human coronaviruses in 825 samples collected before the emergence of SARS-CoV-2, and also examined 389 samples from donors infected with SARS-CoV-2. Combining these analyzes with computer-based models allowed the team to accurately predict the levels of antibodies that would bind and neutralize the invading viruses.

Cross-reactivity reduces the severity of the infection

The researchers were able to demonstrate that people infected with SARS-CoV-2 had lower levels of antibodies against the coronaviruses that cause common colds compared to people who were not infected. On the other hand, people with high levels of antibodies to harmless coronaviruses were less likely to have been hospitalized after contracting COVID-19.

“The study shows that a strong antibody response to human coronaviruses increases the level of antibodies against SARS-CoV-2. Therefore, someone who has gained immunity to harmless coronaviruses is also better protected against severe SARS-CoV-2 infections”, indicated Alexandra Trkola. This type of immune response is called cross-reactivity, and it also occurs with T-cell responses, which are the immune system’s additional line of defense against infection.

People are only fully protected against SARS-CoV-2 soon after recovering from COVID-19 or after receiving an effective vaccine. This is when antibody levels against the virus are still very high. As these levels drop over time, the infection is no longer preventable, but the immune memory quickly reactivates the body’s defenses, antibody production and also T-cell defense.

Infographics: University of Zurich

The investigator clarified that “Immune responses targeting SARS-CoV-2 that are mounted by memory cells are much more effective than cross-reactive responses. But while protection is not absolute, cross-reactive immune responses shorten the infection and reduce its severity. And that is exactly what is also achieved with vaccination, but with much, much more efficiency.”

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Comprehensive protection against coronaviruses

It remains to be seen whether this cross-reactivity also works in the opposite direction. It remains to be clarified whether immunity to SARS-CoV-2 obtained by vaccination, for example, also offers protection against other human coronaviruses. “If immunity to SARS-CoV-2 also offers some degree of protection against infection by other coronaviruses, we would be a significant step closer to achieving comprehensive protection against other coronaviruses, including any new variants,” explained the virologist. This idea is also supported by the fact that protection from cross-reactivity is not only based on antibodies, but very likely on T cells as well.