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.
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.
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.