Research published in the journal Annals of Internal Medicine looked at more than 225,000 people who had been tested for COVID-19 between Jan. 15 and June 30, 2020. Scientists found that people with blood type O negative had a 2.1% chance of testing positive for coronavirus - the lowest probability among all blood groups. The highest probability was in the blood group B positive, at 4.2%.
The researchers found that people with blood type O had a lower chance of severe COVID illness or death compared to people with other blood types.
Additionally, people with Rh-negative blood were found to have a lower probability of both infection and serious COVID-19 illness than people with Rh-positive blood.
"The O and Rh- blood groups may be associated with a slightly lower risk for SARS-CoV-2 infection and severe COVID-19 illness," the researchers concluded.
The results are not entirely surprising. Other peer-reviewed studies have come to the same conclusion about COVID.
And scientists have previously found that certain blood types have seem to be more protective against certain illnesses than others. For example, people with type O blood tend to become sicker from cholera than people with other blood types.
It may be due to antigens, proteins that cover the surface of red blood cells and determine your blood type. When a virus or bacteria enter the body, those antigens trigger the immune system to fight off the invader. Some blood types seem to be more effective sentries than others.
Specific to COVID-19, people with type O blood have a lower tendency to form clots overall. One of the most severe - and poorly understood - complications of COVID-19 is that in some people, the virus causes clotting to form throughout the body, which can cause heart attacks, strokes and pulmonary embolisms, some of which can be fatal.
For now, these are theories that are undergoing further study. But right now, a few things are clear: People with type O blood are not immune from the coronavirus. No matter what your blood type, you should follow all public health recommendations to avoid contracting or spreading COVID-19.
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