Blood Type Has No Impact on COVID-19 Infections or Severity, New Study Finds

There is no link between blood type and COVID-19 susceptibility or severity of illness, a new study published in the Journal of the American Medical Association Network Open shows. These findings contrast with previous studies from China, Spain, Italy, and Denmark, which had shown that individuals with Type A blood were more likely, and individuals with Type O blood were less likely to be infected or become seriously ill with COVID-19.

Researchers at Intermountain Healthcare, a comprehensive health system with 24 hospitals and 215 clinics in Utah, Nevada, and Idaho, reviewed a database of over 107,000 individuals with a documented blood type who received COVID-19 tests between March 3 and November 2, 2020. Of the 107,000 test results on patients with a documented blood type, over 11,000 were positive for COVID-19, and 2,000 of those who tested positive for COVID-19 required inpatient admission to the hospital. Thirty percent of those admitted to the hospital were at one point sick enough to spend time in the intensive care unit.

“We confirmed a higher risk for men, non-whites, and older individuals,” said Jeffrey Anderson, MD, study author and lead researcher. Yet, along all endpoints, researchers found no correlation between blood type and COVID-19 illness.

Anderson speculates several reasons why his team’s research differed from previous study findings. First, other studies had smaller patient sample sizes, predisposing to chance findings, and did not always control for age, ancestry, environment, or geography.

“The harder you try to look for something in a smaller group, the more likely you are to find it,” Anderson says.

Next, Anderson points to publication bias: the likelihood that many journals would not publish a study that found no correlation between ABO blood type and COVID-19, especially if there is no previous research to contradict that finding.

“Other studies didn’t find a relationship, but since that’s neutral, it’s not as appealing to publish,” Anderson says. “Publication bias against negative or neutral studies sets the initial expectation that a non-finding would be bad.”

A third possibility is non-causal associations, i.e., “true, true, but unrelated”. In some but not other populations, blood type might be associated with other, true causal factors, but itself be non-causal. 

Anderson admits that his study population was primarily White and does not match the diversity of the general U.S. population, which could have impacted results. Still, he remains confident in his findings.

“Our results should strictly be applied to a White, northern European ancestry population. I think it would be wonderful for this study to be repeated in a region with a larger African American population to see if the results are the same or different,” Anderson says. “But, I do believe our study is big enough that it rules out any causal impact of ABO blood groups on COVID-19, at least in similar populations.”

Anderson emphasizes that all individuals, regardless of blood type, should continue to wear masks, practice social distancing, wash their hands regularly, and get a COVID-19 vaccine. He adds that ABO blood type should not presently be considered an independent risk factor for COVID disease.

“There are still a lot of unknowns about COVID susceptibility and severity, such as the impact of virus variants, the amount of virus you are exposed to, and the disease’s viral burden, among other things,” he says. “Some people only experience mild symptoms, if that, and others end up on a ventilator and die. We need to keep looking [for explanations]. But don’t be influenced by your blood type into thinking you are better off or worse off.”

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