Why You Shouldn't Put Stock in Reports That Some Blood Types May Be Spared by COVID-19

It's become evident over the past several months that the body's reaction to the novel coronavirus (COVID-19) is quite varied, with some people experiencing only mild symptoms (or no symptoms at all) and others becoming gravely ill. As for why that range is so wide? You may have heard that it could potentially come down to blood type. "Early reports out of China suggested blood type A predicted a poorer outcome from COVID-19," David Cutler, MD, a family medicine physician at Providence Saint John's Health Center in Santa Monica, CA, told POPSUGAR.

However, studies since then have been mixed at best. "One retrospective review showed no significant connection between blood type and worsening of the disease," including important markers like the need for hospitalization, Dr. Cutler explained. "An intriguing finding from the study was that there appeared to be a greater chance of people with blood types B and AB who were Rh positive testing positive for the virus," he continued. "Even stronger evidence was assembled by the team that symptomatic people with blood type O were less likely to test positive."

Months into the pandemic, this seems to be the clearest pattern emerging in the research: that perhaps those with type O blood are less likely to become infected than others. In a Danish study, only 38 percent of COVID-positive patients were type O, even though the same blood type made up nearly 42 percent of a control group, consisting of more than 2 million people from the general population. By comparison, those with type A blood accounted for roughly 44 percent of COVID-19 cases, despite being pretty equally represented in the control group.

Still, experts caution that correlation does not imply causation, and while the findings from various studies on blood types and COVID-19 do seem to be converging, in many cases the research had limitations. "There are many flaws and biases in these studies," Dr. Cutler said. For example, "some studies used blood donors as a comparison group to the COVID-19 patients to look at blood type frequency when COVID-19 is not present. However, it is well known that a disproportionate number of blood donors are type O, as this is the most widely acceptable type of blood for transfusion." Bottom line: early reports aren't conclusive clinical data, and it may be a while before we have the large-scale, long-term studies that would allow experts to draw firm conclusions.

"Due to lack of association between blood type and rates of hospitalization, intubation, or death, I feel it is premature to put too much stock in the topic for now," Daniel Devine, MD, a dual-board-certified internist and geriatrician and cofounder of Devine Concierge Medicine, told POPSUGAR. "This newly identified distinction in infection rate between blood types may be a piece of the larger puzzle of COVID-19. It is a starting point for more research into why the virus overexcites the immune system and why the virus causes blood clots in some people and not others."

If anything, the lack of clear answers is an important reminder that we all need to do our best to follow the guidelines issued by experts and be considerate of immunocompromised and at-risk populations. "Other risk factors seem to play a far bigger role in determining outcome from COVID-19, like age. And there are many known risk factors that can be controlled, like smoking and vaping," Dr. Cutler said. "If these dangerous habits are avoided, outcomes would improve. And no blood type assures complete protection from COVID-19 — however, staying six feet away from people, washing your hands, and wearing a mask are proven to offer excellent protection."

Natasha Bhuyan, MD, family physician and regional medical director at One Medical, agreed. "Since we can't change our own blood type, there isn't much use being worried," Dr. Bhuyan told POPSUGAR. "Instead, we should focus on what we can control when it comes to COVID-19: stay at home when you can, wear a mask when you go out, practice good hand hygiene, and stay six feet away from others."

POPSUGAR aims to give you the most accurate and up-to-date information about the coronavirus, but details and recommendations about this pandemic may have changed since publication. For the latest information on COVID-19, please check out resources from the WHO, CDC, and local public health departments.