Study suggests novel reason for wide range in COVID illness: people never exposed to virus have some antibodies
When researchers in British Columbia tested for antibodies in a small sample of Vancouver residents earlier this year, they found that less than one per cent had definitely been exposed to COVID-19.
That was little surprise, especially at a time when the virus was not spreading widely in the city. But when the scientists delved further, their conclusions were striking.
Large proportions of people who seemingly had never come in contact with the coronavirus, they said, had antibodies that reacted to parts of the bug — that recognized some of the “antigens” in SARS-CoV-2 that switch on a body’s immune system.
If proven valid, the discovery could be a key clue to unraveling one of COVID-19’s remaining mysteries — why infection has little or no effect on some people and yet is devastating to others.
It could also have implications for the effectiveness and safety of vaccines, said Dr. Pascal Lavoie, the B.C. Children’s Hospital scientist who headed the study.
“If what we’re seeing is true, and I believe it is … this could be a major finding,” he said. “It would be crucial to understanding why the virus makes some people sick. … It could (also) guide where you target your vaccination efforts.”
Whether having antibodies to individual SARS-CoV-2 antigens gives people some immunity, or actually undermines their defences against the COVID-19 virus, remains to be seen, said Lavoie.
Such antibodies can sometimes actually help a virus attach to a healthy cell, he said.
He also stressed that the paper, posted on a “preprint” website like many COVID-19 studies, has yet to be peer reviewed and has its limitations.
Indeed, outside experts cautioned Thursday it’s unclear whether the “unusual” findings represent background noise that comes with the testing or true reactivity to the virus.
Lavoie said new data he has just received addresses that concern and appears to make the findings “much stronger.” He plans to submit the study to a peer-reviewed journal soon.
The research needs to undergo that kind of independent assessment to properly gauge whether the findings are valid, said Dr. Mel Krajden, public health lab director at the B.C. Centre for Disease Control.
Even if they are legitimate, he said, it would be “speculative” to suggest that antibodies in unexposed subjects explain the wide range of illness caused by the coronavirus. Age is the clearest predictor now of how sick COVID-19 will make people, noted Krajden.
Lavoie and colleagues asked for volunteers to submit to “seroprevalance” testing — designed to tell if someone has been exposed to a virus — in May and June. They enrolled 276 people, mostly health-care workers.
Of those, only three, or .6 per cent, had antibodies that indicated they had been exposed to the full SARS-CoV-2 virus.
But the “remarkable” finding, the paper said, related to the presence in unexposed people of antibodies to specific antigens in the virus — an antigen being a foreign body that spurs the immune system into action.
About 82 per cent had reactivity to the virus’s famous spike protein, 47 per cent to another of its antigens and seven per cent to a third, the researchers concluded.
Where those antibodies came from is unclear. It might be they’re a result of contracting seasonal coronaviruses, the kind that cause colds, said Lavoie.
But it’s also possible something else entirely produced the antibodies, from bacteria to food, he said.
If the findings are confirmed as accurate, the next step would be to study the links between antibody levels and the severity of illness in people infected by SARS-CoV-2, said Lavoie.
Dr. Catherine Hankins, a McGill University population health professor and co-chair of Canada’s COVID-19 Immunity Task Force, said she wouldn’t read too much into the paper because it’s unclear whether the antibody findings are background noise or true reactivity. Plus, the sample size is tiny compared to some seroprevalence studies that have tested thousands of people.
But she said the question of how antibodies to other viruses might affect a person’s response to COVID-19 — something called cross-reactivity — is an important one.
It’s still murky, for instance, why young children are relatively unaffected by the virus, while elderly people are far more likely to suffer severe cases.
“Is that in any way related to how many times you’ve had a seasonal coronavirus in the past?” said Hankins. “Or have you recently had one because you’re a kid? … Is it the recent activity that protects? We don’t know yet, and these are the questions we want to answer.”
• Email: tblackwell@postmedia.com | Twitter: tomblackwellNP