People with Type A blood are significantly more likely to catch coronavirus than those with Type O, Chinese academics have found.
The study in Wuhan also found those with Type A blood are more likely to die from COVID-19.
In the general population Type O blood (34%) is more common than A (32%). However, among COVID-19 patients, people with Type O accounted for just 25%, whereas Type A made up 41%.
People with Type O blood made up a quarter (25%) of deaths in the research. Normally, Type O people make up 32 percent of people in Wuhan.
The controversial correlation has yet to be scrutinised by other academics in peer review and the researchers are unable to explain why infection varies by blood type.
Researchers in China assessed 2,173 people who had been diagnosed with the coronavirus, including 206 people who died after contracting the virus, from three hospitals in Hubei.
Academics compared the data of the infected Wuhan patients with 3,694 non-infected people in the same region.
Of the 206 patients in the study who died, 85 had type A blood, equivalent to 41 percent of all deaths.
In the healthy Wuhan population, a city of 11 million people, 34 percent of people are type A.
In the study, 52 of the people who died were type O, making up a quarter of all deaths. Under normal conditions 32 percent of people are type O.
The figures for all infections, not just deaths, are 26 percent and 38 percent for type O and type A, respectively.
The coronavirus pandemic has infected almost 200,000 people and killed more than 7,800 worldwide. More than 3,000 deaths were in China.
The researchers write: 'Blood group O was associated with a lower risk of death compared with non-O groups. To the contrary, blood group A was associated with a higher risk of death compared with non-A groups.'
The researchers believe this correlation may reveal type O people are less susceptible to the virus.
'People of blood group A might need particularly strengthened personal protection to reduce the chance of infection,' wrote the researchers in their paper, which has not yet been peer-reviewed but has been published online on medrxiv.
'Infected patients with blood group A might need to receive more vigilant surveillance and aggressive treatment. '
Gao Yingdai, a researcher with the State Key Laboratory of Experimental Haematology in Tianjin, told South China Morning Post: '[The study] may be helpful to medical professionals, but ordinary citizens should not take the statistics too seriously.
'If you are type A, there is no need to panic. It does not mean you will be infected 100 percent.
'If you are type O, it does not mean you are absolutely safe, either. You still need to wash your hands and follow the guidelines issued by authorities.'
The difference in blood groups depends on attachments to red blood cells called antigens. The presence, or absence, of these molecules dictates what blood type a person is.
Previous research has indicates people with types A, B and AB blood have an increased risk of coronary heart disease compared to people with type O blood.
Other research claims people with blood type A have a 24 percent higher risk of heart attack than people with AB or O blood types.