Blood type and Covid-19 infection: is there a link?

The rapid global spread of the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has strained healthcare and testing resources, making the identification of individuals most at-risk a critical challenge. A growing body of evidence suggests that blood type may affect the risk of severe Covid-19. While this may seem odd at first, there are several viral and bacterial pathogens that can lead to chronic diseases and are significantly influenced by blood type. In this article, we will review some of the research that has been conducted regarding Covid-19 and blood type in an attempt to shed some light on this link. 

What is the blood type? 

Let’s start first by looking at the existing blood groups and their main differences. Briefly, there are four main blood types known individually as A, B, AB, or O or collectively as ABO. All cells have a type of glycoprotein on the plasma membrane which is important for cell-to-cell recognition. Pathogenic bacteria and viruses attempt to evade the immune system by trying to masquerade as a host cell inorder to avoid detection. In the context of the immune system, in the immune cell, invasion can occur through the glycoprotein which is a sugar molecule that sits on top of the cell membrane. In response to infection, white blood cells produce antibodies which attach to the antigen, protein molecules that are on the surface of every virus. Antibodies can differentiate between a host cell and a detect a foriegn invader (non-self cell) and upon detection can initiate a cascade of immunological events that help your body fight the offending virus or bacterium. On the surface of red blood cells, there is a specific type of antigen called ‘agglutinogens’ and is a marker used to determine the blood type of a person. For example,  ‘A’ blood type has A antigens, ‘B’ blood type has B antigens, ‘AB’ has both antigens, and ‘O’ has zero antigens none.

As shown in the above diagram, individuals with type A blood produce the ‘A’ antigen and have antibodies that react against type B blood. Individuals with type B blood produce the ‘B’ antigen and have antibodies that react against type A blood. Type AB (the rarest blood type), has both antigens but creates no antibodies whilst type O blood produces no antigens but has antibodies against both A and B. Even though antigens are shown as a few little spikes on red blood cells, each red blood cell has ~2 million of the antigens for the ABO blood type/s (4).  

What does the research on Covid-19 and blood type tell us? 

A recent study has shown that individuals with type O blood are somehow protected from the risk of contracting the novel coronavirus causing Covid-19 compared with individuals who have other blood types. Moreover, scientists also pointed out that those with type O blood are less likely to develop serious illness if they were to become infected  with the virus (1). These findings are similar to an earlier study published in the New England Journal of Medicine in June (6) which showed that individuals with type A blood had a 45% risk increase of contracting the novel coronavirus whilst individuals with type O blood had a 35% decreased risk. Here, researchers studied 1,900 individuals in Spain and Italy who were severely ill with Covid-19 and compared their results with 2,000 individuals who were not ill. Earlier findings from China further support the notion that individuals with type A blood have a higher risk of acquiring Covid-19 compared to non-A blood types, whereas type O blood is linked to a lower risk of infection (10). What’s more, a retrospective analysis from clinical features in 101 death cases with Covid-19, demonstrated that the ABO blood group distribution of deaths differed pretty remarkably between the Han population in Wuhan. Although not analysed statistically, type O blood type was comparatively less frequent with type A blood being more frequent among the deaths (3). 

Indeed, these numerous findings have led scientists to worry that individuals with type A blood may have increased anxiety surrounding Covid-19 whilst those with type O blood may become down or too unconcerned and thus not take social distancing or government guidance as seriously. 

Why are there differences among blood types and Covid-19 infection? 

Whilst this topic is still a matter of debate, there may be an explanation as to why non-O blood types seem to be more susceptible to Covid-19 infection and seem to have worsened disease outcomes. In fact, it’s possible that some of the protection for type O blood types as well as some of the increased risk for type A blood types may be similar to the mechanisms that have suggested with SARS-CoV-1, namely the fact that type A antibodies have been shown to provide some protection by inhibiting the interaction between the SARS-CoV-1 virus and the angiotensin-converting enzyme 2 (ACE2) receptors - the virus’s primary entry site into the cell (5, 6). In other words, your red blood cells are covered with molecules that are known as antigens which help prompt a response from your body’s immune system. So, it could be argued that antigens for individuals with type O blood block the spike protein in SARS-CoV-2, the virus that causes Covid-19, and blocks it from entering into your cells. Furthermore, blood types can also serve as receptors for different viruses and bacteria meaning that there may be some other completely different components of type O blood that works to prevent infection. This may be due to the presence of both anti-A and anti-B antibodies, as present in the type O blood, which may help neutralize the SARS-CoV-2 to effectively protect the body from becoming infected (9). 

What does all of this research mean for you? 

There have been numerous suggestions, especially around social media, stating that individuals with type 0 blood don’t need to worry as much about Covid-19. Likewise, there have also been rumors about extra cautions that individuals with type A, B, and AB may need to take. But, scientists disagree on this matter. In fact, there is no real benefit linked to your blood type, and you may still acquire Covid-19 independently of it (2). So, while it may be tempting to want to run out and get your blood tested, research is still being conducted to understand the biological mechanisms related to the ABO blood type association first. This link may be clearer in the future, but for now, testing your blood type to find out whether you may be more susceptible to Covid-19 is currently not recommended (7).  

The take-home message 

Although interesting, these findings cannot be used to lessen the serious precautions that everyone needs to take regardless of their blood type. Whilst there appears to be a reduced risk of being hospitalised with Covid-19 if you are a type O blood, this does not mean guaranteed protection against Covid-19. Instead, the type of reduction in risk achieved with appropriate social distancing and hand hygiene is significantly better than depending on your blood type for protection. For this reason, there is absolutely no place for type 0 people to be complacent about general public health advice.

References 

1. Barnkob, M., Pottegård, A., Støvring, H., Haunstrup, T., Homburg, K., Larsen, R., Hansen, M., Titlestad, K., Aagaard, B., Møller, B. and Barrington, T., 2020. Reduced prevalence of SARS-CoV-2 infection in ABO blood group O. Blood Advances, 4(20), pp.4990-4993.
2. Boudin, L., Janvier, F., Bylicki, O., and Dutasta, F., 2020. ABO blood groups are not associated with the risk of acquiring SARS-CoV-2 infection in young adults. Haematologica, 105(12).
3. Chen, J., Fan, H., Zhang, L., Huang, B., Zhu, M., Zhou, Y., Yu, W., Zhu, L., Cheng, S., Tao, X. and Zhang, H., 2020. Retrospective analysis of clinical features in 101 death cases with COVID-19. medRxiv.
4. Dean L. Blood Groups and Red Cell Antigens [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2005. Chapter 5, The ABO blood group. Available from: https://www.ncbi.nlm.nih.gov/books/NBK2267/
5. Guillon, P., Clément, M., Sébille, V., Rivain, J.G., Chou, C.F., Ruvoën-Clouet, N. and Le Pendu, J., 2008. Inhibition of the interaction between the SARS-CoV spike protein and its cellular receptor by anti-histo-blood group antibodies. Glycobiology, 18(12), pp.1085-1093.
6. New England Journal of Medicine, 2020. Genomewide Association Study of Severe Covid-19 with Respiratory Failure. 383(16), pp.1522-1534.
7. Romagnoli, S., Peris, A., De Gaudio, A.R., and Geppetti, P., 2020. SARS-CoV-2 and COVID-19: between pathophysiology complexity and therapeutic uncertainty. Physiological reviews.
8. Storry, J.R., and Olsson, M.L., 2009. The ABO blood group system revisited: a review and update. Immunohematology, 25(2), p.48.
9. Wu, B.B., Gu, D.Z., Yu, J.N., Yang, J., and Shen, W.Q., 2020. Association between ABO blood groups and COVID-19 infection, severity, and demise: A systematic review and meta-analysis. Infection, Genetics, and Evolution, 84, p.104485.
10. Zhao, J., Yang, Y., Huang, H., Li, D., Gu, D., Lu, X., Zhang, Z., Liu, L., Liu, T., Liu, Y., He, Y., Sun, B., Wei, M., Yang, G., Wang, X., Zhang, L., Zhou, X., Xing, M. and Wang, P., 2020. Relationship between the ABO Blood Group and the COVID-19 Susceptibility.
11. Zietz, M., Zucker, J., and Tatonetti, N., 2020. Associations between blood type and COVID-19 infection, intubation, and death. Nature Communications, 11(1).