MIT Medical answers your COVID-19 questions. Got a question about COVID-19? Send it to us at CovidQ@mit.edu, and we’ll do our best to provide an answer.
I have read that people with certain blood types are more susceptible to contracting COVID-19. My understanding is that people with Type O blood are less susceptible than people with other blood types. Is this true? And would my blood type be part of my record at MIT Medical — maybe from lab work I’ve had done in the past? If so, how can I get that information?
The question of a possible relationship between blood type and disease risk has been a topic of active research since early in the pandemic. The first hint of a possible relationship came in March, from researchers in China, who compared nearly 2,200 hospitalized COVID-19 patients to a control group of approximately 27,000 healthy individuals. They observed that individuals with Type A blood appeared to be at significantly higher risk of contracting the virus — constituting nearly 38 percent of the ill patients, compared with the 31 percent of healthy individuals with this blood type. The risk for individuals for Type O blood appeared to be significantly lower, just 26 percent of the cases versus 34 percent of the healthy control group. Individuals with Type A blood type also represented a higher percentage of patients who succumbed to the illness — 41 percent versus 25 percent for Type O.
In April, researchers at Columbia University reported similar risks associated with Type A blood after blood-typing more than 1,500 New Yorkers and testing them for COVID-19. While the distribution of blood types is different in New York City than in Wuhan and Shenzhen, after controlling for other risk factors, they found that individuals with Type A blood were 34 percent more likely to test positive for the coronavirus, while having Type O or AB blood was associated with a lower probability of testing positive. However, they did not find strong evidence for a relationship between blood group and risk of intubation or death.
Both of these studies were posted to the MedRxiv website, where researchers share preliminary, unpublished data, before it has undergone peer review. However, a genome-wide association study (GWAS) recently published in the New England Journal of Medicine (NEJM) is both consistent with, and potentially explains, these earlier results. GWAS is a methodology used in genetics research to identify specific genetic variations associated with particular diseases. The NEJM study analyzed genetic data from more than 1,600 patients who had been hospitalized with severe cases of COVID-19 in Italy and Spain and compared them with about 2,200 uninfected individuals. The analysis turned up gene variants in two regions of the human genome that were associated with severe illness and greater risk of COVID-19-related death. One of these areas contains genes that determine blood type along with other genes that are known to be associated with immune function.
And, in fact, these researchers, like the researchers in China and New York City, found a higher risk for severe illness among individuals with Type A blood and a protective effect for Type O. Type A blood was associated with a 45 percent increased risk of having respiratory failure, while Type O was associated with a 35 percent reduction in risk.
The reason behind this association remains unclear. The authors of the NEJM study hypothesize that different combinations of A and B antigens may change how the immune system produces infection-fighting antibodies or have some other, unknown effect on how the body responds to infection. Or, they suggest, perhaps the genes associated with blood type also have some effect on the ACE2 receptor, the protein that allows the SARS-CoV-2 virus to infect human cells.
As far as determining your blood type, it’s unlikely to be part of your medical record at MIT Medical. Our clinicians do not order blood typing routinely, other than for pregnant patients. If your clinician has ordered medically necessary blood typing for you in the past, the result would be available in your patient portal. If not, you can order an inexpensive kit to test your blood at home by pricking your finger to get a small blood sample, which you can then mix with antibodies to the A and B antigens that come on the card. But an even better way to get your blood type tested is to donate blood, which, by the way, is still a safe thing to do, even during a pandemic.
Of course, your blood type is not a risk factor over which you have any control. You shouldn’t panic if you have Type A blood, and you shouldn’t feel complacent if you’re Type O. These studies are fascinating from a scientific perspective, but at this point, they have no practical implications for the way we live our lives and the precautions we should be taking to protect others and ourselves. So, keep wearing that mask, socially distancing, and washing your hands — actions that are proven to reduce the risk of illness for people of every blood type.