Scientists have found a connection between blood type and a person’s susceptibility to Covid-19. While the results are still very much preliminary for now, it’s not the first piece of research to highlight such a link.

Scientists at the biotech giants 23andMe have recently studied over 750,000 people, including 10,000 that were hospitalized and diagnosed with Covid-19, to see whether genetic data could provide any insights into their condition. The results have not been formally published nor peer-reviewed yet, but the preliminary findings have unearthed some interesting information.

Firstly, people with blood type O appear to be less susceptible to Covid-19. While that doesn’t mean people with blood type O have some kind of superhuman protection against the disease, they are 9-18 percent less likely than individuals with other blood types to have tested positive for Covid-19, according to the data.

Looking specifically at people who had a high probability of exposure to the virus, such as healthcare workers, the researchers found 3.2 percent of participants with blood type O tested positive for Covid-19, while 3.9 percent of blood type A tested positive, 4 percent for B, and 4.1 percent for AB. After adjusting for age, age squared, sex, race, ethnicity, body-mass index, and other factors, blood type O showed to have a slight but notable “protective effect” against both acquiring Covid-19 and being hospitalized for the infection, according to a statement by 23andMe.

However, there are a number of other parameters that were not investigated and the link is so far a correlation with no indication of a causal link, so we have to take the findings with a hefty pinch of salt for now.  

"There have also been some reports of links between Covid-19, blood clotting, and cardiovascular disease. These reports provided some hints about which genes might be relevant,” Adam Auton, a principal scientist at 23andMe, told Bloomberg. "It's early days; even with these sample sizes, it might not be enough to find genetic associations.”

"We're not the only group looking at this, and ultimately the scientific community may need to pool their resources to really address questions surrounding the links between genetics and Covid-19," Auton added.

All caveats aside, the research is largely in line with the few other studies on the topic. Another study of hospital patients in the Chinese city of Wuhan, where the pandemic is thought to have begun, showed that blood group A was associated with a higher risk of Covid-19 compared with non-A blood groups, while blood group O was associated with a lower risk. Researchers in Italy and Spain also reached similar conclusions in a new pre-print study.

"Importantly, people should not panic about these results as clearly further scientific research is required to substantiate these claims," Dr Sakthi Vaiyapuri, Associate Professor in Cardiovascular and Venom Pharmacology at the University of Reading, who was not involved in any of these studies, said in March 2020 while commenting on the blood type study from Wuhan.

Edited 12/06/2020: The fourth paragraph of this article has been edited for clarity and accuracy.