Jun 8, 2020 - Research

Blood type may play a role in COVID-19 


Editor’s note 9/5/23: Thanks to all our readers for their questions on this post. Please note, 23andMe does not currently offer a report on blood type, and our COVID-19 research is now complete. See the findings from our COVID-19 Study here.

Preliminary data from 23andMe’s ongoing genetic study of COVID-19 appears to lend more evidence for the importance of a person’s blood type — determined by the ABO gene — in differences in the susceptibility to the virus.

While 23andMe researchers continue to explore the implications of this data, we’re also continuing to provide important genetic health information to our customers. Compare our DNA tests to learn more about our services.

23andMe is still recruiting for its massive study, most recently seeking 10,000 participants outside of 23andMe who have been hospitalized and diagnosed with COVID-19. (Note: Currently, only those living in the U.S. are eligible to participate in this study.) 23andMe researchers have yet to finish looking at what the genetic data indicate.

A First Look

But a first blush look at the information from the more than 750,000 participants in the study shows the following:

  • The preliminary data suggest that O blood type appears to be protective against the virus when compared to all other blood types.
  • Individuals with O blood type are between 9-18% percent less likely than individuals with other blood types to have tested positive for COVID-19, according to the data.
  • There appeared to be little differences in susceptibility among the other blood types.
  • These findings hold when adjusted for age, sex, body mass index, ethnicity, and co-morbidities.
  • Although one study found the blood group O only to be protective across rhesus positive blood types, differences in rhesus factor (blood type + or -) were not significant in 23andMe data. Nor was this a factor in susceptibility or severity in cases.
  • Among those exposed to the virus — healthcare and other front line workers — 23andMe found that blood type O is similarly protective, but the proportion of cases within strata is higher.

Preliminary Genetic Association

While it is still very early in the study, 23andMe’s preliminary investigation into genetics seems to support these findings. We’ve compared the research participants who reported that they tested positive for COVID-19 to those who tested negative. Our researchers identified a variant in the ABO gene associated with a lower risk. (The single nucleotide polymorphism in the ABO gene is rs505922, a T at that location is associated with lower risk. The P-value for the association is 1.4e-8, OR = 0.88).

Both the data on blood type and the preliminary genetic findings also appear to support at least two recently published pre-print studies — one by researchers in China and the most recent one by researchers in Italy and Spain — that look at the ABO gene’s role in COVID-19. The study in China looked at susceptibility, while the Italian and Spanish study found an association with blood type and severity of the illness.

Numerous other studies have reported that the ABO blood group plays a role in both susceptibility and severity for COVID-19 (refs: 1, 2, 3). We know from other studies that the ABO blood group can play a direct role in other types of infections. This is because it serves as receptors, or coreceptors for microorganisms, parasites, and viruses. The preliminary findings from 23andMe’s data are also notable because of the link between COVID-19 blood clotting, and cardiovascular disease.

Comparing Blood Types

23andMe researchers wanted to investigate this link with blood type, so we estimated the contribution to risk by comparing each blood group against each of the others. Because the differences are quite small, an extremely large sample size is needed to explore differences across groups. For 23andMe’s study, which now includes more than 750,000 individuals, we investigated the cumulative incidence of self-reported COVID-19 by blood type, hospitalization by blood type, and proportion of those infected after known exposure by blood type.

Here is what we found.

A chart showing the percent of 23andMe research participants who tested positive for COVID-19 by blood group
Percent of 23andMe research participants who tested positive for COVID-19, by blood group.

Among respondents to the 23andMe COVID-19 survey, the percent of respondents reporting a positive test for COVID-19 is lowest for people who are O blood type. The percent of respondents reporting a positive test for COVID-19 was highest among those with the AB blood type.

Those who were blood groups A, B, and AB did not statistically differ from each other (Table 1 Below). This relationship holds after adjusting for age, sex, body mass index, race, ethnicity, and co-morbidities.

Looking at Those with Higher Probability for Exposure to COVID-19

One study found the blood group O protective only across rhesus positive blood types. But in 23andMe’s data we found that differences by self-reported rhesus factor (blood type + or -) were not significant. Neither was the interaction between blood group and rhesus factor in statistical models predicting being a case, or being a hospitalized case.

To better understand the risk of acquiring the infection, we restricted the data to those with a high probability of exposure. This included professional health care workers. These would be individuals with close contact with known cases, and essential workers. As you can see below, blood type O shows a similar pattern as seen above. But the proportion of cases within strata is higher, as we would expect.

After adjustment for age, age squared, sex, race (census race categories), ethnicity (Hispanic or Latino), BMI, and a single variable indicating a vulnerability to severe infection (e.g. high-risk co-morbidity or immunocompromised) blood type O showed a protective effect against both acquiring (OR = 0.86, p < 0.0001), and being hospitalized for the infection (OR = 0.81, p = 0.05). The protective effect of acquiring the infection strengthened in models restricted to the “exposed” population (OR = 0.81, p < 0.0001). (Table 1).

A chart showing cases and controls and the odds ratios
Table 1. Adjusted Odds Ratios (ORs) and 95% Confidence Interval (CI) estimating the effect of blood type O compared to all other blood types for the risk of infection (case v control) or hospitalization. An OR is a statistic that quantifies the strength of the association between a measurement and an outcome, while a Confidence Interval is a range of values that is likely to contain the true unknown value.

In the whole population, those with the O blood group were 9-18% less likely to test positive compared to the other groups. When looking at only exposed individuals, those with O blood group were 13-26% less likely to test positive.

A chart showing blood type for people exposed to COVID-19

Still Recruiting

23andMe launched its COVID-19 study on April 6th. We invited customers to participate in the large-scale study looking at whether genetics could help explain the differences in severity among patients.

A chart showing the percent of those exposed to COVID-19 who were diagnosed with it.
Percent reporting positive test for COVID-19 among those with a high probability of exposure (health care professionals, essential workers, and those experiencing personal contact with a diagnosed case), by blood group.

In May, the study was expanded. We added individuals outside of 23andMe who have experienced severe COVID-19 symptoms. The expanded study, in which 23andMe is providing 10,000 kits free of charge, aims to identify individuals who tested positive and were hospitalized for COVID-19. As part of the research, participants answer survey questions. These are questions about whether they’ve experienced cold or flu-like symptoms for instance. We also ask whether they’ve been diagnosed or treated for COVID-19, and whether they’ve been hospitalized for the illness.

The study and recruitment are ongoing. We hope that we can use our research platform to better understand differences in how people respond to the virus. Ultimately, we hope to publish our research findings. We want to provide more insight into COVID-19 for the scientific community.

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