Race and ethnicity remain significant risk factors for infection and severe outcomes.
As scientists searched for patterns in who fell ill during the early pandemic, a large genetic study offered a quiet but telling signal: blood type, that ancient biological classification, appeared to carry a modest influence over COVID-19 susceptibility. 23andMe's analysis of over one million participants found that people with type O blood were measurably less likely to test positive, while type A individuals showed greater vulnerability — a difference possibly rooted in how certain antibodies interact with the virus. Yet the study's most sobering finding had nothing to do with blood: African Americans who contracted COVID-19 were nearly twice as likely to be hospitalized as white patients, a disparity that persisted even after accounting for income and underlying health, pointing toward structural inequities far older and more consequential than any genetic marker.
- A 23andMe study of over one million people found type O blood associated with 9 to 18 percent lower COVID-19 infection risk, with the protective effect growing stronger among frontline workers with the highest exposure.
- The proposed mechanism — that anti-A antibodies in type O blood may block the virus from binding to cells — offered a plausible but contested explanation, with other studies finding conflicting results or no meaningful difference in antibody effectiveness across blood groups.
- Beneath the blood-type headline, a far more urgent pattern surfaced: Black Americans who tested positive were nearly twice as likely to require hospitalization, a disparity that held even after adjusting for sex, income, and pre-existing conditions.
- Latino populations showed similarly elevated hospitalization rates, with researchers pointing to structural inequities in healthcare access, housing, and economic stability as the deeper drivers of severe illness.
- Scientists cautioned that blood type is a minor variable in a complex equation — having type O is no license to relax precautions, and having type A is no cause for alarm — while behavioral safeguards remain the most reliable protection for everyone.
In the early months of the pandemic, researchers began noticing a pattern: blood type seemed to correlate with COVID-19 risk. Biotech company 23andMe, drawing on its vast genetic database, set out to test whether the ABO blood group system — the same one used to match transfusion donors — might predict coronavirus susceptibility. Their findings, first released as preliminary data in mid-2020 and later expanded to over one million participants, suggested that people with type O blood were 9 to 18 percent less likely to test positive. Among healthcare workers and other high-exposure groups, the protective effect was even more pronounced.
The leading theory pointed to antibodies. Type O blood carries both anti-A and anti-B antibodies, and prior research had suggested that anti-A antibodies might interfere with the virus's ability to bind to host cells — which would explain why type A individuals appeared more vulnerable. 23andMe released its findings as a pre-print, sharing the data openly before peer review to help accelerate the global search for treatments.
The picture, however, was not so simple. Other researchers found conflicting results: one study suggested type O individuals might simply be underrepresented in COVID-19 samples, distorting the apparent effect. A meta-analysis confirmed the blood-type trend but found no link between blood type and disease severity or death — a crucial distinction.
What the data revealed far more sharply was a disparity rooted not in genetics but in society. African Americans who tested positive were nearly twice as likely as white Americans to be hospitalized, and even after adjusting for income, sex, and underlying health conditions, Black patients remained 80 percent more likely to require hospital care. Latino populations showed a similar pattern. Senior 23andMe scientist Janie Shelton noted that race and ethnicity remained among the most significant risk factors in the entire dataset.
The blood-type finding, while scientifically intriguing, was ultimately a minor thread in a much larger story. Researchers were careful to stress that the effects were small, the evidence mixed, and that no one should alter their behavior based on their blood type alone. The pandemic, the data made clear, would not yield to a simple biological shortcut.
In the early months of the pandemic, as researchers scrambled to understand why some people seemed to weather COVID-19 better than others, a pattern began to emerge in the data: your blood type might matter. The biotech company 23andMe, which had been collecting genetic information from millions of people, decided to look at whether the ABO blood group system—the same classification that determines compatibility for transfusions—correlated with coronavirus risk. What they found, released first as preliminary data in June 2020 and later expanded into a full pre-print study, suggested that people with type O blood had a measurable advantage.
The initial analysis covered 750,000 participants, including 10,000 people hospitalized with COVID-19 from outside 23andMe's own user base. Those with type O blood were 9 to 18 percent less likely to test positive for the virus than people with other blood types. When researchers narrowed the focus to healthcare workers and other frontline staff—people with the highest likelihood of exposure—the protective effect grew even more pronounced: type O individuals showed 13 to 26 percent lower infection rates. By the time 23andMe published its expanded findings, the dataset had grown to over one million participants, making it one of the largest genetic studies of COVID-19 susceptibility attempted to that point.
The biological mechanism behind this difference, researchers theorized, lay in the antibodies present in different blood types. Type O blood carries both anti-A and anti-B antibodies in the plasma, whereas type A blood has only anti-B antibodies and type B has only anti-A. Previous research had suggested that anti-A antibodies could actually inhibit or block the virus from binding to host cells—a finding that would explain why type A individuals appeared more vulnerable. The theory was plausible enough that 23andMe decided to release its findings as a pre-print, sharing the data openly with the global research community before peer review, in hopes of accelerating the search for treatments and vaccines.
But the picture was more complicated than a simple blood-type story. Other researchers who examined the same question found conflicting results. One study suggested that type O individuals might simply be underrepresented in COVID-19 research samples, skewing the apparent protective effect. Another analysis of antibodies across blood groups found no meaningful difference in their ability to fight the virus. A meta-analysis that reviewed all available evidence at the time did confirm that type A appeared more susceptible and type O less at risk, but found no clear link between blood type and disease severity or mortality—a distinction that mattered for how people should interpret the findings.
What emerged more starkly from 23andMe's data, however, was a disparity that had nothing to do with blood type. African Americans who tested positive for COVID-19 were nearly twice as likely as white Americans to require hospitalization. Even after researchers adjusted their analysis to account for sex, income, and underlying health conditions—factors that might explain some of the difference—Black patients remained 80 percent more likely to be hospitalized. Latino populations showed a similar but slightly less pronounced pattern. These gaps pointed to something deeper than genetics: structural inequities in health care access, living conditions, and economic vulnerability that made certain communities far more susceptible to severe illness.
Janie Shelton, a senior scientist at 23andMe, underscored this reality in a statement accompanying the findings: race and ethnicity remained among the most significant risk factors for both infection and the most severe outcomes requiring hospitalization. The blood type story, while scientifically interesting, was ultimately a minor player in a much larger drama. The researchers themselves cautioned against over-interpreting their results. The protective or susceptibility effects associated with blood type, even if real, were small enough that many other factors clearly mattered far more. Having type A blood was no reason to panic, and having type O blood was no reason to let your guard down. The pandemic, the data suggested, was not going to be solved by knowing your blood type.
Notable Quotes
Race and ethnicity still stand out as a significant risk factor for infection with COVID-19 as well as for the most severe symptoms that require hospitalization.— Janie F. Shelton, Senior Scientist at 23andMe
The Hearth Conversation Another angle on the story
Why did 23andMe decide to study blood type and COVID-19 in the first place? It seems like an odd connection.
They had the data already—millions of people who'd provided genetic information. When the pandemic hit, they could cross-reference that with COVID test results. It's a natural question for a genetics company to ask.
And they found type O people were less likely to get sick. That's a pretty clean result. Why the skepticism?
Because other researchers couldn't replicate it cleanly. Some found type O people were just underrepresented in the studies, which would create a false pattern. Others looked at the antibodies directly and found no real difference. Science doesn't move in straight lines.
But the meta-analysis did confirm the pattern, right?
It did, for infection risk. But not for severity or death. That's important—it means even if blood type matters a little, it doesn't determine outcomes the way people might hope.
So what was the real story in their data?
The racial disparities. Black Americans hospitalized with COVID were almost twice as likely to need hospitalization as white Americans. That number didn't go away even when you controlled for income and health conditions. That's the finding that actually changed how we understood the pandemic.
Why does that matter more than blood type?
Because it points to something fixable. Blood type is fixed. But the conditions that made Black and Latino communities more vulnerable—that's about systems, not biology.