Type O Blood Linked to Lower Rates of COVID-19 (2024)

Ongoing research indicates that people with type O blood seem to have a slightly lower risk of contracting COVID-19.

While it’s too soon to know why type O blood offers a protective effect against the disease, several studies suggest there is a correlation. One of the largest data sets on the topic comes from the genetic testing company 23andMe, which has surveyed over a million people since April. The company’s survey data shows that people with type O blood are 9% to 18% less likely to test positive for COVID-19 than people with other blood types.

“We think this finding is going to be really essential to the scientific community to understand the biological mechanism behind COVID-19 susceptibility: Why do some people get impacted and not others?” Anjali Shastri, PhD, Senior Research Program Manager at 23andMe, tells Verywell. “Being able to uncover that mechanism can help them understand the disease better, and then treat it down the road.”

23andMe plans to publish a paper for the scientific community in the coming weeks. Shastri says the company’s user behavior gave them a unique opportunity to do so.

“As a company with expertise in genetic research and this amazing cohort of highly-engaged individuals, we wanted to run a study to see if there’s any genetic basis to why we were seeing differences in the susceptibility and the severity of COVID-19,” she says.

Shashtri says phase 1 of the study began with a survey of 750,000 existing 23andMe customers. When researchers filtered the data down to respondents with the highest likelihood of COVID-19 exposure—including healthcare workers, those with close contact to known cases, and essential workers—the protective effect of type O blood appeared even stronger. Potentially exposed respondents were 13% to 26% less likely to test positive compared to people with other blood types who were potentially exposed.

The study’s careful phrasing of “less likely to test positive” poses a question: Is there a chance people with type O blood are somehow more prone to false-negative results from COVID-19 diagnostic tests? Shashtri doesn’t think so.

“We haven’t identified any reason why the O blood type would test negative more often,” she says. “We control for a whole host of factors, including [false negatives], and we don’t see that effect.”

Other Blood Types and COVID-19

The 23andMe data only shows that people with type A, AB, and B blood are more likely to test positive compared to those with type O blood. Between these three blood types, there is no difference in COVID-19 susceptibility.

Other Research Exploring Blood Type and COVID-19

23andMe researchers are not the only ones exploring the relationship between blood type and COVID-19. A study of 2,173 patients with COVID-19 in China—published ahead of print on March 27—found both a higher risk of COVID-19 in people with type A blood and a lower risk in people with type O blood.

Another pre-print study of 1,980 COVID-19 patients in Spain and Italy, published on June 2, found a protective effect of type O blood against respiratory failure related to COVID-19.

Shortly after 23andMe released their initial findings highlighting the protective effect of type O blood on June 8, a group of Harvard Medical School Researchers at Massachusetts General Hospital corroborated that people with type O were less likely to test positive for COVID-19.

The Harvard researchers tracked 1,289 patients who tested positive for COVID-19 from March 6 through April 16. Their results, published on June 12 in the Annals of Hematology, include another important finding: Blood type does not appear to be associated with risk of disease progression to severe cases of COVID-19.

23andMe is still in the process of exploring the relationship between blood type and COVID-19 severity. Most of their survey respondents who reported testing positive for COVID-19 experienced only mild or moderate symptoms. For phase 2 of their work, the company is now recruiting 10,000 people who are not 23andMe customers who have both tested positive for COVID-19 and been hospitalized.

“The idea here is to really hone in on and capture the spectrum of severity,” Shashtri says. “To really understand severity, we want to focus on those individuals who had previously been hospitalized.”

How Data Is Collected Without a Blood Sample

If you’ve ever taken a 23andMe test, you know it relies on a saliva sample. And nowhere in your results does it mention blood type. So how did researchers draw their conclusions? Shashtri says they came up with their own sort of dual authentication process.

“Basically, we did two analyses,” she says. “One was looking at self reports. That relied on individuals telling us what their blood type was. We correlated that with the test positives and severity.”

The second analysis relied on data that 23andMe is able to collect from saliva samples but doesn’t currently include in any consumer-facing reports. This analysis of a single nucleotide polymorphism (SNP) determined whether an individual had type O blood.

Shashtri says her team was able to compare this SNP data to user-reported information about blood type to help corroborate genetic information.

While asking for self-reported data from so many participants can have drawbacks like recall bias—errors in accuracy based on incomplete or inaccurate recollection—Shashtri says her team feels their data is accurate so far.

“All of our findings are based on self-reported phenotypes [characteristics]. But what’s really encouraging is we are coming up with the same findings as researchers based on clinics,” Shashtri says. “The study that first reported the O blood type finding was looking at hospitalized patients in Italy and Spain. The fact that we’re finding the same results makes us pretty confident.”

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.