Covid infection: Scientists think blood type plays a role, and have identified which one is least at risk

• Your blood type may predict how severely you'd be affected by Covid-19, should you catch infection.
• This is according to two recently published studies.
• The findings are based on patient data from Denmark and Vancouver, Canada.

People with blood type O are less likely to become infected with Covid-19, the disease caused by SARS-CoV-2, according to two new studies published in the journal Blood Advances.

They are also at lower risk of severe Covid-19 outcomes, such as organ failure, and even death.

Scientists have been investigating a potential link between blood type and vulnerability to Covid-19 for many months, and this latest evidence supports previous findings.

A preprint study published in March this year suggested that people with blood type A have a higher risk of acquiring Covid-19 compared with non-A blood groups, while another study published in June found that blood type O seemed to be more resistant against Covid-19 infection.

First study: Denmark

In this study, researchers analysed data from a Danish health registry that included more than 473 000 people who were tested for Covid-19 between 27 February 2020 and 30 July 2020. A total of 7 422 individuals tested positive. After controlling for certain factors, they found fewer patients with blood type O, compared with patients with blood types A, B, and AB.

The researchers also point out that they did not find any significant difference in rate of infection between A, B, and AB blood types.

They also controlled for ethnicity, as blood group distributions differ among ethnic groups, and maintained that fewer people with blood type O tested positive for Covid-19.

"It is very important to consider the proper control group because blood type prevalence may vary considerably in different ethnic groups and different countries," said study author Torben Barington, MD, of Odense University Hospital and the University of Southern Denmark.

"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."

Separate study: Canada

Researchers of this study found that Covid-19 patients with blood groups A and AB had an increased risk of severe clinical outcomes, compared to patients with blood groups O or B.

In this study, researchers investigated data from 95 critically ill, hospitalised Covid-19 patients in Vancouver, Canada, who were admitted to the intensive care unit (ICU) between 1 March 2020 and 28 April 2020.

A total of 38 patients had blood types A or AB, and 57 had blood types O or B.

They wrote that patients with blood groups A or AB were more likely to require mechanical ventilation (34, or 84%) versus those with blood group O or B (35, or 61%), which means that their risk of lung injury from Covid-19 was greater.

More than this, the research team also found that more of these patients required dialysis for kidney failure.

The researchers also wrote that their study’s findings are congruent with a recent study of 1 980 Covid-19 patients that also demonstrated a link between ABO blood type and disease severity.

However, both studies’ authors note several limitations that warrant consideration, and suggest further research to confirm these findings and enhance scientists' understanding of blood type association to Covid-19 severity.

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