Claim: People with blood type A are more likely to catch the coronavirus

Outlets have reported that people with type A blood type are more likely to contract the new coronavirus, although many failed to emphasize that the research lacks peer-review, a large sample size and that experts have told the public not to be concerned.

The claim gained popularity through a series of widely shared Facebook posts. Its momentum has continued with Science Focus, MSN, the South Florida Sun Sentinel and local broadcast news outlets in Iowa and Virginia running stories.

Newsweek, Express, Science Alert and Medical News Today also published stories on the findings.

What experts say: It's premature to assume there is a link

The claim is based on new research from a group of medical experts at hospitals and universities in China. The researchers come from an array of institutions, including the National Clinical Research Center for Infectious Diseases, the Renmin Hospital at Wuhan University and the School of Medicine at the Southern University of Science and Technology in China.

The study was published in March on medRxiv, a nonprofit founded by the Cold Spring Harbor Laboratory, Yale University and BMJ. MedRxiv is a preprint server where researchers share preliminary findings before peer review. The model makes research accessible to other experts without having to wait for the often-lengthy peer review and journal publication process.

Researchers studied 2,173 people from three hospitals in Wuhan and Shenzhen, China, who tested positive for the coronavirus.

Their conclusions showed 37.75% of the sampled people were blood type A, 26.42% were blood type B, 10.03% were blood type AB and 25.80% were blood type O. These data, when compared to the proportions of blood groups of the public in the region, led researchers to conclude that blood group A was more susceptible to the virus than other blood groups, while blood group O had a lower chance.

But this research has not been peer reviewed or published in a medical or academic journal, which means other experts in the field have not analyzed its research methodology, citations or significance. Its intent is primarily to “generate debate among experts,” PolitiFact wrote.

“Preprints are preliminary reports of work that have not been certified by peer review,” medRxiv’s site reads. “They should not be relied on to guide clinical practice or health-related behavior and should not be reported in news media as established information.”

Preet Chaudhary, chief of hematology at the University of Southern California, said the research is not conclusive because researchers didn't replicate their results. On page 7 of the study, a trial with 285 patients from Shenzhen did not show blood group A to be more susceptible. He also said differences between the blood groups of the noninfected group and the group with COVID-19 were only a few percentage points.

"It’s only marginal basically," Chaudhary said. "This is preprint. It’s not published yet. Let it get published and let it get peer reviewed."

Chaudhary expressed concern that the findings may prompt people with blood type O to be less cautious due to the possibility that they may be less susceptible.

Sakthivel Vaiyapuri, associate professor at the University of Reading in the United Kingdom, said in a statement to PolitiFact that the research should be ignored because it lacks scientific validation and may cause individuals with blood type A to panic.

"It’s better to safely ignore any article that hasn’t been properly scrutinized by peer review and published in a rigorous scientific journal," Vaiyapuri said in the statement.

The South China Morning Post covered the findings and interviewed Gao Yingdai, a researcher with the State Key Laboratory of Experimental Haematology in Tianjin who was not involved in the study and critiqued the research. She said the study would be stronger with a larger sample size. A sample of 2,000 is not necessarily small, but is only a fraction of the nearly 700,000 confirmed cases worldwide as of March 30, according to the World Health Organization.

Gao also said the study lacked a clear explanation for the phenomenon “such as the molecular interaction between the virus and different types of red blood cells.”

Our ruling: False

Although this research shows the possibility of a link between blood type and susceptibility to the virus, the research has not been peer reviewed or published in an academic journal and relies on a relatively small sample size. Multiple experts, as well as the site on which the research is published, have advised against deeming the link as being established.

There is not enough evidence to definitively state a relationship between blood type and susceptibility to the new coronavirus.

Our fact-check sources:

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