Blood type O may offer some protection against COVID-19, two studies suggest

Type A at more risk; mechanisms poorly understood
Posted at 2:40 PM, Oct 16, 2020
and last updated 2020-10-16 21:16:45-04

SAN DIEGO (KGTV) — Two new studies published this week suggest people with blood type O have a lower likelihood of catching COVID-19 and developing severe illness than people with other blood types.

Blood type is a characteristic we inherit from our parents and there are four major blood groups: A, B, AB and O.

Danish researchers looked at nearly 500,000 people who tested positive for COVID-19 and found that people with type O were underrepresented.

In a study published in the journal Blood Advances, the researchers found 38.4 percent of those infected had type O when that type actually makes up 41.7 percent of the population in that area.

The researchers say the findings suggest people with type O are less likely to get infected in the first place.

On the other hand, the team found that people with type A blood were overrepresented: 44.4 percent of those infected had type A compared to an expected value of 42.4 percent. The researchers suggest people with type A might be more at risk.

Another study, also published in Blood Advances, looked at 95 critically ill patients in Canada. They found people with type O or type B blood tended to have a shorter stay in the intensive care unit, an average of nine days for those blood types compared to 13.5 days for people with type A or AB.

They also reported that people with type O or type B were less likely to need a ventilator, with 61 percent of cases requiring mechanical ventilation compared to 84 percent for people with blood type A or AB.

“Yes, there may be some of these associations. I don't think it's fully understood at this point,” said Dr. Christian Ramers of Family Health Centers of San Diego, who was not involved in the studies.

The science on COVID-19 risk and blood type is mixed. These two new studies align closely with a previous study in China and another in Europe, but a third study in the U.S. found no significant link between severe COVID cases and blood type.

At this point, doctors aren’t sure why blood type might affect outcomes with the disease, but there are several theories.

“The immune system is an incredibly mysterious and complicated thing that we don't fully understand,” Ramers said. “Blood type sort of plays into that because people with different blood types actually have slightly different immune systems and immune responses.”

Your blood type impacts the kind of antibodies you produce. That is why it is so important in blood transfusions to get the right blood type; blood from the wrong donor can trigger antibodies that attack those red blood cells.

People with blood type O have two sets of antibodies, known as anti-A antibody and anti-B antibody. People with type A or B only have one or the other.

Researchers in the Canadian study hypothesized that the anti-A antibody in particular may help control the coronavirus. People with blood type O and blood type B produce this kind of antibody. Individuals with type A or type AB do not.

People with blood type O also have characteristics that make them less prone to issues with blood clotting, a major issue in severe cases of COVID-19.

Experts say that if type O blood is protective against the virus, it’s not by a large amount.

And this protective benefit doesn’t extend to all pathogens. Past studies have shown people with type O are more at risk from a type of bacteria that can cause ulcers and cholera.