Researchers have found that some antibodies picked up from seasonal “common cold” coronaviruses might also target SARS-CoV-2, the virus that causes Covid-19.

Most intriguingly, these cross-reactive antibodies appear to be more prevalent among kids, which the researchers speculate could go towards explaining why children appear to be less vulnerable to severe Covid-19 infections. Although it’s too early to tell the full implications of this discovery, it holds some very interesting possibilities. 

As reported in the journal Science, scientists at the Francis Crick Institute in the UK discovered that many people who had never been infected with Covid-19 appeared to have antibodies in their blood that recognized and responded to SARS-CoV-2. This is particularly surprising since antibodies to specific viruses are typically created after the body’s immune system has had a run-in with the pathogen. Instead, it appears that some people may develop antibodies that respond to SARS-CoV-2 through other seasonal “common cold” coronavirus infections they've picked up over their lifetime. 

“Along with the new SARS-CoV-2 strain, there are a number of other strains of coronavirus circulating in the human population that cause nothing more than a cold,” Kevin Ng, lead author and post-graduate student in the Retroviral Immunology Laboratory at the Crick, told IFLScience.

“While SARS-CoV-2 and these common cold coronaviruses are only distantly related, they share certain structural similarities. These are the parts of the virus that can be targeted by antibodies generated during a common cold.”

To confirm their findings, the researchers analyzed over 300 blood samples collected in the UK between 2011 and 2018, long before the pandemic took hold. As expected, they noted most of these samples had antibodies that reacted to common cold coronaviruses, such as OC43, 229E, NL63, HKU1. They also noticed that about 5 percent of these samples also had antibodies that cross-reacted with SARS-CoV-2 in a petri dish. Interestingly, these cross-reactive antibodies were found in up to 45 percent of children under 17, most likely because they’d had more recent exposure to seasonal coronaviruses compared to adults.

It's an intriguing and important discovery. However, it’s unclear yet whether these cross-reactive antibodies will prevent SARS-CoV-2 infection or spread. Although the antibodies respond to the SARS-CoV-2 in a petri dish, the researchers say it’s too early to say whether they will provide any meaningful protection in the human body. 

“It's definitely too early to tell at this point. Epidemiological studies of SARS-CoV-2 infection and spread are inconsistent with cross-reactive antibodies playing a large role – the antibodies may play some role in reducing symptoms, but on the flip side there are some suggestions that these antibodies could make things worse,” explained Ng. 

“We would definitely like to speculate that these antibodies are part of the reason children seem to present with milder symptoms, though once again I stress that this is purely hypothetical at this point.”

Furthermore, Ng stressed that the study’s findings do not back up the so-called “herd immunity” approach to the Covid-19 pandemic, noting that it doesn’t mean that children are immune to the disease. It also doesn't necessarily mean that people who have had common colds will be any less vulnerable to Covid-19. 

“We certainly shouldn't be deliberately infecting ourselves with common colds as a vaccine either,” he added.