Can antibodies against seasonal coronaviruses protect against COVID-19 ?

Although SARS-CoV-2 is a new coronavirus, the majority of people have already been exposed to other seasonal coronaviruses. Having been infected by a seasonal coronavirus does not seem to protect against SARS-CoV-2, but only reduces the risk of developing a severe form of the illness. The origin of this possible relative cross-protection between coronaviruses is however not well understood. The aim of the study described here was to quantify the level of antibodies directed against seasonal coronaviruses and to see if they are linked to protection against SARS-CoV-2.

American researchers at the University of Pennsylvania analyzed the serum of 431 individuals before the COVID-19 pandemic so as to quantify cross-reaction antibodies reacting against SARS-CoV-2. 20% of these individuals had antibodies reacting against the spike (S) protein or the SARS-CoV-2 nucleocapsid protein. No differences were observed due to the ages of the donors. The majority of these individuals had antibodies targeting seasonal coronaviruses but these levels were higher in those who had cross-reaction antibodies against SARS-CoV-2.

The serum of 251 individuals who were later infected by SARS-CoV-2 was analysed before the pandemic. Once again, 20% of these individuals had cross-reaction antibodies before the pandemic which were able to react against SARS-CoV-2, that is, the same percentage as in the wider population. This shows that the presence of these antibodies does not protect against infection by SARS- CoV-2. In addition, no correlation could be found between the levels of these antibodies and the severity of COVID-19. However, infection by SARS-CoV-2 increases the level of antibodies directed against these seasonal coronaviruses.

So these results show that, even though cross-reaction antibodies originating from former infections by seasonal coronaviruses exist, and react against SARS- CoV-2, these antibodies are unable to protect against infection or against severe forms of COVID-19.