A case of COVID-19 can be from mild to severe. Sometimes no symptoms are present, sometimes people die. More and more studies suggest that blood types may play an important role by affecting immune responses.
Why do some people not notice at all that they have contracted the coronavirus, while others require medical treatment — and, in the worst cases, even die?
That COVID-19 seems so unpredictable also makes it difficult to find out how many people are actually infected and how many have already built up immunity. The number of unreported cases is correspondingly high.
Already in June, German and Norwegian researchers analyzed different blood types with regards to COVID-19. They came up with some informative results, which they published in the New England Journal of Medicine.
The researchers investigated the role blood type might play in patients with particularly severe forms of the disease.
In the study, the researchers examined 1,610 patients with COVID-19 respiratory failure in Italy and Spain, where the coronavirus hit particularly hard: Milan, Monza, Madrid, San Sebastian, and Barcelona. All patients were struggling with particularly severe cases, and some did not survive.
A first result: People with blood type A seem to be at a particularly high risk of a severe case of COVID-19. In Germany, 43% of the population has this blood type. In the event of coronavirus infection, these individuals might be two times more likely to need an oxygen supply or respirator than people with blood type O: 41% of Germany's population.
Blood type O may be able to consider themselves lucky as things stand. Even though they are not protected against an infection, the study shows they have the lowest risk of coming down with a severe case of the disease.
People with blood type O- (O negative) also play a special role as blood donors, as they are considered "universal donors" and can help anyone in need of a blood transfusion.
Blood types B and AB are not as widespread, making up just 11% and 5% of the population, respectively. According to the study, the likelihood of a severe COVID-19 diagnosis for these groups could lie somewhere between that of people with blood types O or A.
Since then, further studies have been added to confirm the original results. On 14 October, two studies appeared in the journal Blood Advances, here and here, which also show less severe symptoms of the disease in people in blood group O. Simultaneously, the Medical University of Graz independently reported aseries of experiments, designed to further investigate the phenomenon.
The results of the studies may help in developing various drug treatments. Researchers have used similar approaches when searching for medication to fight other diseases.
In the case of malaria, for example, scientists have established a link between the disease and different blood types. For example, it is now known that people with blood type O very rarely develop severe malaria and are very well-protected against its most severe form.
In the case of other diseases, other blood types protect the human body best. For example, with the bubonic plague, people with blood type A showed the mildest symptoms.
For a long time, COVID-19 research focused on high-risk patients: Those who have certain preexisting conditions and/or have reached a certain age. Smokers also came under scrutiny as a potentially high-risk group. Now, researchers are looking at a different piece in the coronavirus jigsaw puzzle.
Note from the editors: This article has been updated since its original publication to reflect information gathered from new scientific studies.