The studies add to the mystery of blood groups.

We have at least 42 different blood group systems, including A, B, AB and O. Their prevalence differs around the world in ways that dont seem random. Some raise and lower a person's risk of various diseases.

And despite the A, B, AB and O groups being discovered almost 120 years ago, scientists still do not fully understand their purpose.

The answer to that question wins a Nobel prize, said Professor David Irving, director of research at the Australian Red Cross Blood Service.

The newest study linking COVID-19 risk to blood-type is from 23andMe, one of the pioneers in commercialised genetic testing. Members send 23andMe a spit sample and get back a DNA report.

The company with permission keeps that DNA on its database for research. That gives it the unique ability to quickly run huge genetic studies.

"Its re-energised the debate about what the role of the blood group system is."Credit:Red Cross Lifeblood / Supplied

A survey by 23andMe of its 1.05 million members asked if they had tested positive to COVID-19. It compared those results with their genome, looking for patterns.

The company found a protective association between having type O blood and the chance of testing positive.

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"Any difference is not huge," said Dr Alison Gould, the Red Cross' scientific communications specialist. "Were not talking immune."

The study was uploaded to research site medRxiv last week. It has not yet been peer reviewed or published in an academic journal, meaning its findings need to be treated with caution.

There are a number of theories as to be why someone's blood type has a bearing on the chances of them catching coronavirus.

Humans get their blood groups from a set of marker molecules on the surface of red blood cells. Each blood group has its own marker.

But these markers dont just show up in the blood. They are also, for reasons scientists dont understand, on cells all throughout the body including in the nose and throat.

SARS-CoV-2 uses its spike protein to attach to a cell, like a key sliding into a lock. It is possible different blood marker molecules might get in the way of that attachment.

Red blood cells with a white blood cell.

"You've got the lock and key. But youve also got a range of other things sitting around that lock. And those may help or hinder the key getting into the lock," said Dr McFadyen.

Professor Irving called this hypothesis unlikely. The more likely culprit, he said, was "molecular mimics".

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Similar marker molecules used for blood types show up, thanks to chance mutations, on the surface of a diverse range of viruses.

People naturally develop antibodies to the blood groups they do not possess.

Perhaps SARS-CoV-2 has marker molecules that look a bit like those on type A red blood cells.

That would mean people with type O blood would have antibodies that could attack the virus, while people with type A would not.

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Liam is The Age and Sydney Morning Herald's science reporter

The rest is here:
The story of O: Blood type may lower your chances of catching COVID - Sydney Morning Herald

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