A person’s blood type may play a part in how likely they are to catch coronavirus and how severely the disease impacts them, new research suggests.  

People with type O are less likely to catch Covid-19 or develop major complications and die. Meanwhile, individuals with blood types A and AB are most vulnerable to the disease, two independent studies have found. 

The findings could shed further light on why the illness proves deadly for some but others are not even aware they have had it.

One team compared Danish health registry data of over 473,000 individuals tested for Covid-19 to a control group of more than 2.2 million from the general population.

There were fewer positive results among those with blood type O – the most common – and more in peers with A, B and AB, while rates of infection were similar in those three groups.

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Researchers also took ethnicity into account, since it affects blood group distributions.

Lead author Dr Torben Barington, of Odense University Hospital, said: ‘It is very important to consider the proper control group because blood type prevalence may vary considerably in different ethnic groups and different countries.

‘We have the advantage of a strong control group – Denmark is a small, ethnically homogenous country with a public health system and a central registry for lab data. So our control is population-based, giving our findings a strong foundation.’

A second study of 95 critically ill Covid-19 patients in hospital in Vancouver found the A and AB blood types were at higher risk of severe symptoms than those with O or B.

They were more likely to require mechanical ventilation – suggesting they had greater rates of lung injury from the virus – and dialysis for kidney failure.

It suggests these two blood groups have an increased risk of organ dysfunction or failure due to Covid-19.

And while people with blood types A and AB did not have longer overall hospital stays, they remained in the intensive care unit (ICU) for longer on average.

The Canadian researchers suggest that may may also signal a more severe illness.

Lead author Dr Mypinder Sekhon, of the University of British Columbia, said: ‘The unique part of our study is our focus on the severity effect of blood type on Covid-19.

‘We observed this lung and kidney damage, and in future studies, we will want to tease out the effect of blood group and Covid-19 on other vital organs.

‘Of particular importance as we continue to traverse the pandemic, we now have a wide range of survivors who are exiting the acute part of Covid-19, but we need to explore mechanisms by which to risk stratify those with longer-term effects.’

Experts have long said age and weight are key factors in how severely impacted patients are.  

Scientists have been looking into the question of whether blood type has a significant link to infection and illness severity. The two papers, published in the journal Blood Advances, add to evidence of a link.

Earlier this year, a study of more than 2,000 coronavirus patients in China found that of the 206 who died, 85 had blood type A – equivalent to 41%.

It also showed they were more vulnerable to infection and tended to develop more severe symptoms. Those with blood type O had a ‘significantly lower risk’ of getting the disease.

The Chinese team urged medics and governments to consider blood type differences when treating patients with the virus and helping prevent the spread of the disease.

Almost half of the UK population (48%) has O type blood.

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