Today I participated in another radio call in show about COVID-19. I was stumped by a question regarding ABO blood type and susceptibility to COVID-19. Did having Type A blood make you more likely to get sick when infected with SARS-CoV-2?

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I was fully prepared to discuss the ibuprofen story, but this was news to me. Thanks to a long commercial break, I was able to look it up. A few days ago, Chinese researchers uploaded a pre-print to medrxiv. They looked at more than 2000 COVID-19 patients in hospitals in China, including some who had died. They found that patients with blood type A were associated with a higher risk of infection than those with blood type O. They also had a higher risk of death. Since there are more people in the general population with type O than with type A, this wasn’t simply a reflection of the population. (Types B and AB also had higher risk than O, but the difference wasn’t statistically significant.)

Does this mean that being Type A is bad? Not necessarily. First rule of epidemiology is correlation does not equal causation. Coincidence happens in science too.

SARS-CoV-2 infects the lungs, so why would blood type even matter?

Interestingly, a similar pattern was found for SARS-CoV, the virus that caused the SARS outbreak in 2003–2004. Having Type A blood means you have a molecule on the surface of your cells that Type O lacks. People with Type O blood have naturally occurring antibodies to Type A blood. This is why someone who has Type A blood can’t donate to someone with Type O. The Type O person’s immune system will recognize that A surface molecule as foreign and attack it with “Anti-A antibodies.Researchers studying SARS-CoV hypothesized that these anti-A antibodies also recognized the spike (S) protein on the surface of the coronavirus, blocking infection, or at least providing some protection.

So that brings us back to the question, if you have Type A blood, do you need to worry? Maybe, but not necessarily. The difference (37.75% Type A vs 25.80% Type O) is statistically significant. But what this means isn’t really clear. It’s an interesting story and worthy of further research, but maybe not a determining factor in disease. There are other co-morbidities linked to higher risks.

This story does highlight the importance of understanding the scientific reports during an outbreak in context. medRxiv is an extremely useful resource for scientists. It’s a site developed by Yale and Cold Springs Harbor Laboratory for researchers to upload articles as soon as they write them, before peer-review. In a typical scientific journal, articles go through extensive review by multiple scientists who will point out weaknesses, inaccuracies, or just ask hard questions for clarity. In an outbreak situation, we need information fast, and we don’t have the months available to go through that process.

That doesn’t mean we shouldn’t trust the articles in medRxiv because they’re not peer reviewed. It means we need to understand that they are preliminary. Such research is often meant to pose more questions than it answers. This is what scientists do- we ask questions. Sometimes those questions lead to groundbreaking research. And sometimes, they don’t.

So if you have Type A blood (like me), don’t fret. Take all your usual precautions. Wash your hands. Be alert to symptoms. Practice appropriate social distancing. Review the science.

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