Study links blood type to severity of virus

People with blood type A are at significantly higher risk of developing severe Covid-19, according to a study that has teased out the genetic factors that may explain why some people are so much worse affected by the virus.

The research, accepted for publication in a peer-reviewed journal, looked at the genomes of more than 1600 people admitted to hospital with Covid-19 who needed help breathing, and compared them with those who had not contracted the disease.

Those who had blood type A appeared to be as much as 50 per cent more likely to need oxygen or a ventilator. About 42 per cent of Britons have blood type A.

The finding adds to other evidence in China that suggested blood type, which is genetically determined, may increase both susceptibility and severity. Findings from the genetics company 23andMe also imply a related corollary: that having blood type O is actively protective, good news for the estimated 44 per cent of people in the UK with that type.

Andre Franke, professor of molecular medicine at Christian-Albrechts University of Kiel, said that it was still not clear why blood type was involved in this way.

Since his research was published, prior to peer review, he said he has heard a lot of theories from other scientists.

‘‘Now this is on the radar everywhere, people are looking very closely at it.’’

It may be because of the biology of the blood itself, he said, or it may be because the genes that determine the blood also have other effects.

He and his colleagues found other genes that appeared to be linked to Covid19, but some of the most interesting findings were in those that were not.

‘‘I was very surprised in the beginning. Everyone in the scientific community, if they were asked where they would put their money, would have said chromosome 6,’’ he said.

This is a region linked to the immune system and implicated in many infectious diseases. But there was no signal there. Neither was there a link to the cell receptor ACE2, used by the virus to enter the body.

The study was not perfect. Ideally there would be another full group of patients for comparison who were infected but who did not develop the severe disease.

This was one reason, said Professor Franke, that he could not be confident of the exact risk increase linked to blood type: ‘‘It may be 20 per cent, it may be 30 per cent, it may be 50 per cent.’’

He said that they chose to work faster as they realised speed was of the essence. ‘‘You need to know what’s going on if you want to fight the disease. Vaccination is very important but we also need a treatment for people who are infected, who go along the route to severe disease.’’

Finding a genetic link will suggest drug targets and also give clues as to who should be treated more aggressively from the beginning.

For individual people who are not infected, however, he said it should not be a cause for undue concern. ‘‘I get a lot of emails from people who say, ‘I’m very worried to go out because I’m blood group A’.

‘‘It’s clear something is going on, that this is involved in disease.’’ But, he said, other factors such as obesity outweighed genetics.

‘‘And while there are many people in hospital with blood group A, there are also many with blood group O. Everyone must pay attention.’’ –