Blood Types and Their Newfound Significance in COVID-19
By: Jason Yang
Tags: Research, Covid 19, Health, Science, Medicine

Red Blood Cells by AllInOneMovie via Pixabay

As a kid, I got bitten a lot by mosquitos. My arms and legs would be covered in red bumps one day, followed by me putting little cross marks on them the next day to help lessen the itchiness. It wasn’t until adulthood that I learned mosquitoes are attracted to higher body temperatures, sweat, certain clothing colors, and, surprisingly, blood types.

How are blood types involved? In 1974, scientists found that mosquitos may prefer those with blood type O more than others. Interestingly, blood types have been implicated in a variety of diseases as well. Some examples include H. pylori infection, which is a bacterial infection that causes ulcers, and norovirus infection, which is a viral infection that causes the common “stomach bug” [reviewed here].

On June 8, 2020, blood types again came under the spotlight. 23andMe, a personal genomics company, announced preliminary results from their massive 750,000-people-study looking at genetic differences and COVID-19 infection rates. The news was covered by Wall Street Journal, Bloomberg, and a brief mention from New York Times.

On June 17, 2020, New England Journal of Medicine published a study asking similar questions but aimed at patients from Spain and Italy. This news garnered attention from the media as well, giving us coverage from Reuters, CNN, and CBS.

The news coverage centered around one finding: some blood types may lead to an increased risk for COVID-19 while others may lead to a decreased risk.

But how were these studies conducted? Are there limitations to the findings? How should we interpret these results? Here, I will break down these studies in hopes of answering those questions, and we will begin with a brief review of blood types.

What is a blood type?

Introduction to Blood Types by SciShow

Our blood is made up of red blood cells, white blood cells, platelets, water, proteins, and different solutes like sodium and potassium. The red blood cells carry oxygen from our lungs to different parts of our bodies to keep everything going. On the surfaces of those red blood cells, there are antigens that identify a cell to our immune system.

Blood type is the antigen that resides on our red blood cells.

Blood Types by InvictaHOG via Wikipedia

Considering the table above, having type A blood means I have the A antigen. It also means I have antibodies against the B antigen.

The reason for these antigens and antibodies is because our immune systems want to ensure we have our own red blood cells. After all, red blood cells carry out one of the most important functions in our bodies — delivering oxygen to our muscles and brain. If somehow blood of a different blood type comes into our body, our immune system wants to detect it and use antibodies to destroy them to preserve our own red blood cells.

Taking it a step further, this immune response is also why we do blood typing before giving or receiving blood. For example, if I have blood type O and receive blood type A, B, or AB, then the antibodies in my body, which are targeting against antigens A and B, will attack the red blood cells of any other type of blood. Conversely, because my red blood cells don’t have any antigens on them, my blood can be accepted by any other person. By the same logic, those with AB blood type can receive any blood because they don’t have any antibodies.

Photo by Andre Mouton on Unsplash

There is another set of antigens called “Rh,” and people can be “Rh positive” or “Rh negative.” It was named after the Rheusus monkey in error, but the shorthand Rh has stuck around. It goes along with the blood types we saw from above, and it is noted as “+” or “-.” So, you can be A+ or A-, B+ or B-, AB+ or AB-, or O+ or O-. While we won’t go into details here, its significance is most apparent during pregnancy.

Table 2. Frequency of blood types among Americans. Source: American Red Cross

Finally, we will round up with a little discussion on the frequency of blood types among Americans. According to the American Red Cross, for Caucasians, Type O+ and A+ share the lead almost equally. For African Americans and Latino Americans, type O+ dominate. For Asians, type O+ still is the most frequent, but type A+ and B+ share the second place together. Regardless of the race, type O+ is overall the most frequent blood type.

Now that we understand what a blood type is, let’s take a look at the studies.