Pre-existing coronavirus antibodies could protect against new COVID-19 strains

Researchers have found that some antibodies, created by the immune system during infection with common cold coronaviruses, can also target SARS-CoV-2 and may confer a degree of protection against the new viral strain. The study was conducted at the Francis Crick Institute and University College London, both UK. 

The researchers explain that in response to infection with a virus, the immune system creates antibodies to help fight it. These antibodies remain in the blood for a period after infection and in the case of re-infection, they are able to tackle the virus again. 

The scientists found that some people, notably children, have antibodies reactive to SARS-CoV-2 in their blood, despite not ever having being infected with the virus. They suggest that these antibodies are likely the result of exposure to other coronaviruses, which cause a common cold and which have structural similarities with SARS-CoV-2.

The researchers made this discovery while developing highly sensitive antibody tests for COVID-19. To see how well their assay tests were performing, they compared the blood of patients with COVID-19 to patients who had not had the disease. They found that some people who had not been exposed to SARS-CoV-2 had antibodies in their blood which would recognise the virus. To confirm their findings, they analysed over 300 blood samples collected before the pandemic, between 2011 and 2018. 

Nearly all samples had antibodies that reacted with common cold coronaviruses. However, a small fraction of adult donors, about one in 20, also had antibodies that cross-reacted with SARS-CoV-2 and this was not dependent on recent infection with a common cold coronavirus.  

Notably, such cross-reactive antibodies were found much more frequently in blood samples taken from children aged six to 16.

Kevin Ng, lead author, said: “Our results show that children are much more likely to have these cross-reactive antibodies than adults. More research is needed to understand why this is, but it could be down to children being more regularly exposed to other coronaviruses. These higher levels we observed in children could also help explain why they are less likely to become severely ill with COVID-19. There is no evidence yet, however, that these antibodies prevent SARS-CoV-2 infection or spread.”

In the lab, the researchers tested the antibodies they found in blood from uninfected people to confirm they are able to neutralise SARS-CoV-2. They found the cross-reactive antibodies target the S2 subunit of the Spike (S) protein on the surface of the virus.

George Kassiotis, senior author, said: “The S of this coronavirus is made of two parts or subunits, performing different jobs. The S1 subunit allows the virus to latch onto cells and is relatively diverse among coronaviruses, whereas the S2 subunit lets the virus into cells and is more similar among these viruses. Our work shows that the S2 subunit is sufficiently similar between common cold coronaviruses and SARS-CoV-2 for some antibodies to work against both. It was previously thought that only antibodies to the S1 could block infection, but there is now good evidence that some antibodies to S2 can be just as effective. This is exciting as understanding the basis for this activity could lead to vaccines that work against a range of coronaviruses, including the common cold strains, as well as SARS-CoV-2 and any future pandemic strains.”

The researchers say that a large study is now underway to uncover the role that different antibodies and other immune defences play in protection against COVID-19 and how severely ill people become. 

The paper was published in Science.