PEOPLE with certain blood types are more likely to catch the coronavirus and die from it, scientists say.
Their findings, using data from more than 225,500 people, add to mounting evidence that blood type is a risk indicator for Covid-19 disease.
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There are four blood groups – A, B, AB and O. A person can either be positive or negative, meaning there are eight types in total.
What blood type you are will depend on the genetics from your parents.
The most common blood group in the UK is O, making up almost half the population.
And the majority of Britons are positive (85 per cent). Therefore type O+ is the most common blood type in the UK.
The rarest blood group is AB, accounting for three per cent of people. Only one per cent of the population are AB-.
The latest study involved thousands of volunteers in Canada. They had all had a blood test between 2007 and 2019 to determine their type.
Participants had also had a Covid test between January and June of this year.
HOW DO YOU FIND OUT YOUR BLOOD TYPE?
GPs do not routinely do tests for people's blood groups.
Sometimes a healthcare professional will check your blood type for medical reasons or if you need a blood transfusion.
You can find out your blood group if donate blood, which only one in 25 people do, according to the NHS.
Your blood group will be checked if you give blood through NHS Blood and Transplant, and it will be recorded on your official donor card.
This is so your blood can be matched to someone with the same blood should they need it.
Blood is made up of red blood cells, white blood cells and platelets in a liquid called plasma.
Your blood group is identified by antibodies and antigens in the blood.
To work out your blood group, your red cells are mixed with different antibody solutions.
If, for example, the solution contains anti-B antibodies and you have B antigens on your cells (you're blood group B), it will clump together.
If the blood does not react to any of the anti-A or anti-B antibodies, it's blood group O.
A series of tests with different types of antibody can be used to identify your blood group.
If you have a blood transfusion – where blood is taken from one person and given to another – your blood will be tested against a sample of donor cells that contain ABO and RhD antigens.
If there's no reaction, donor blood with the same ABO and RhD type can be used.
How common is each blood type?
There are eight main blood types but some are rarer than others. The list below shows the percentage of donors with each blood type:
- O positive: 35 per cent
- O negative: 13 per cent
- A positive: 30 per cent
- A negative: 8 per cent
- B positive: 8 per cent
- B negative: 2 per cent
- AB positive: 2 per cent
- AB negative: 1 per cent
Data from NHS Blood and Transplant, accurate at December 2018.
The researchers used blood group A as a reference for how likely people were to catch the coronavirus.
After taking into consideration all the other risk factors for Covid-19, scientists said those with type AB blood were 15 per cent more likely to test positive for the virus compared with type A.
And those in type B group were 21 per cent more likely than type A to get the virus.
People in A and AB blood groups appear to be at a greater risk of infection and the worst Covid-19 outcomes.
Infection is five per cent less likely in type O than A. However, when this group was compared with all blood groups, this grows to 12 per cent.
The researchers also found those who have a negative blood type (O-, A-, B- or AB-) are 21 per cent less likely to be struck with the disease, on average.
Taking the findings into account, people who were O- were 16 per cent less likely than all others to be infected with the coronavirus.
But the study didn’t give a breakdown for the other groups.
Worse outcomes
In the study cohort, there were 1,328 cases of severe Covid-19 illness or death.
Those who were in AB (the rarest) and B blood groups were more likely to suffer the worst outcomes of the disease – 21 per cent more likely than those in group A.
Meanwhile, those in group O were six per cent less likely than group A to deteriorate, jumping up to 13 per cent less likely compared to all blood groups.
Negative types were also 18 per cent less likely than positive types to get severe Covid-19 or die.
The study suggests that people with AB+ or B+ blood are the most at risk of severe Covid-19 outcomes, while those with O- are the least.
But the study did not confirm this due to the way it was designed.
Mounting evidence
The Canadian researchers wrote in their paper: “Taken together, the current body of evidence suggests that O and Rh− (negative) blood types may protect against SARS-CoV-2 infection and, possibly, severe COVID-19 illness.
“Whether this information can influence COVID-19 prevention or treatment strategies remains to be determined.”
The findings, published in the journal Annals of Internal Medicine, chime with a Danish study which found fewer positive test results among those with blood type O and more in peers with A, B and AB.
The researchers had compared 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.
Another 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.
Another study of Italian and Spanish people found the risk of needing ventilation for Covid-19 was 35 per cent lower in people with O blood compared to other groups.
Similarly an Iranian hospital found O blood had a 32 per cent lower risk of being hospitalised with Covid-19.
But not all the studies done so far have taken variables such as pre-existing illnesses into account, which may skew the results. And some have not been peer-reviewed by other scientists to check for mistakes.
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