SARS-CoV-2 immunity looks stronger than many expected.

Three pieces of good news from publications that together indicate that immunity obtained from infection with SARS-CoV-2 will protect against further infection, COVID illness, and from infecting other individuals with the virus.

The first study in the journal Science examines rhesus macaques infected with SARS–CoV-2. All of the animals who were infected had clinical illness compatible with COVID infection including high levels of virus in the upper and lower respiratory tract. The animals also had pathologic evidence of viral pneumonia.

These animals all developed humoral and cellular immune responses typical of a viral infection. When re-challenged with SARS–CoV-2 virus none of the animals showed evidence of clinical infection, including pneumonia, and the small amount of virus that was identified by PCR appeared to be the result of the viral challenge and not new viral production.

These results definitively show that SARS–CoV-2 virus infection provides immune protection against reinfection. Importantly, the immune response occurs rapidly to control subsequent exposures, as would be expected from a memory response due to the previous infection.

Two additional studies also showed important evidence of protection in humans after COVID. A publication in the journal Cell documented that individuals infected with SARS-CoV-2 have strong cellular immunity that was directed against multiple proteins in the virus. This immunity was what would be necessary to clear the virus from secretions and cells especially after a secondary exposure. Of interest, approximately half the individuals who have not been infected with SARS-CoV-2 have cellular reactivity to the virus.  It is possible that immunity to the pandemic coronavirus might be induced by cross reaction from other viral infections such as the “common cold” coronaviruses.

These results suggest that the cellular response to SARS-CoV-2 is adequate to protect against reinfection and that even individuals who haven’t been exposed to the virus may have some degree of immunity. This latter, unexpected finding might indicate why so many individuals have mild or asymptomatic infections during this pandemic.

Finally, prior data from Korea raised concerns that individuals could be re-infected after developing immunity to SARS-CoV-2. A new study from the Korean Center for Disease Control and Prevention (KCDC) refutes that concern. The KCDC examined patients who had developed immunity after confirmed COVID illness and SARS-CoV-2 infection. There was no evidence of recurrent illness or the ability to infect anyone in these individuals. It therefore appeared that the positive PCR (swab) test for virus was because of dead virus or viral remanence identified in the individuals.

Together, these results show that immunity to SARS-CoV-2 virus is strong and protective in all individuals who get infected. It also refutes the concept that individuals who develop immunity can get re-infected. All good news about the future benefit of herd immunity on this pandemic.