COVID-19: Exploring the impact for people with different ABO blood types
COVID-19 is the disease caused by a specific type of coronavirus, called SARS-CoV-2.
Are you at increased risk for COVID-19?
Researchers have found that your blood type may (slightly) increase your risk.
Before continuing, I must impress upon the reader how important it is for everyone to practice social distancing during the COVID-19 pandemic, regardless of your own personal risk for infection, illness, or death.
This pandemic is just ramping up and we are currently experiencing 1,000 global deaths per day, even with the ongoing efforts to curtail the loss of life.
A friend shared with me the following research study, first posted to the medRxiv.org on March 11, 2020. The authors investigate the relationship between the ABO blood types, infection by the SARS-CoV-2 coronavirus, and patient death. Follow along to review their study and explore their findings. Readers should note that manuscripts submitted to medRxiv are not peer-reviewed, edited, or typeset before being posted online.
Let’s take a look at what the authors actually studied.
As described, the research cohort was composed of 2,173 patients with the COVID-19 disease (confirmed by SARS-CoV-2 test) from across two areas in China (Wuhan and Shenzhen), including 206 patients who died. Recent surveys of ABO blood type distribution from 27,080 people without COVID-19 in the same two parts of China were used as comparison controls. Importantly, the researchers report no significant difference in patient age among different ABO blood types.
Here is this data set, without the stats, and I’ll suggest you return to the paper at the link above, if you want to scrutinize the stats for yourself.
The authors state the small sample size is a limitation. Critics will note the percentages for patients with A, B, and AB blood types are inconsistently higher and lower than comparison controls. Indeed, it is difficult to draw conclusions for these blood types, even though the A, B, and AB blood types seem to trend towards greater risk for infection than comparison controls.
However, it is notable that percentages for patience with O blood type are consistently lower than the comparison controls, suggesting people with O blood type may have a reduced risk for infection by SARS-CoV-2.
The reason for people with O blood type having potentially reduced risk for infection by the coronavirus that causes COVID-19 is not immediately clear, and this is what we will explore for the remainder of this thread.
Note, however, that this potentially reduced risk is so slight that it should be completely ignored for the current pandemic, unless you are a researcher looking to exploit a weakness in the virus.
Why people with O blood type may be at reduced risk for infection by the SARS-CoV-2 coronavirus
We don’t yet have enough data yet to adequately assess whether people with O blood types are at reduced risk for infection by the SARS-CoV-2 coronavirus. Until we have that data, we also won’t know the impact on susceptibility to or mortality of the resulting CORVID-19 disease.
Nonetheless, we will dive into the scientific literature and explore some reasons why O blood types might be impacted different from A, B, and AB blood types.
First, we need a primer on blood types, viruses, and antibodies!
On the outer surface of red blood cells are molecular structures which define whether your blood type is A, B, AB, or O. These structures are chains of sugar molecules — see the ⬡ shapes in the image to the left.
Every blood type starts with the same four sugar molecules, so the terminal sugar ⬡ is what distinguishes each ABO blood type. The terminal sugars for A and B blood types have similar shapes, differing in only a few atoms… whereas O blood type is completely missing a sugar!
(For specific chemical names, check out the caption on this image.)
These chains of sugar molecules )-⬣-⬣-⬣-⬣-⬣ can physically bind to molecules outside the cell in the bloodstream. This is similar to casting a fishing line and reeling in whatever bites the hook. Take a look at the video below to see this in action with a protein antigen.
There are many types of sugars and proteins which sit on human cell surfaces, and viruses can reach out to bind them.
Similarly, all coronaviruses have outer shells, and just like human cell surfaces, these coronavirus shells are covered in sugars and proteins.
One of these proteins is the Spike glycoprotein (left), which is used by all coronoviruses to infect cells. The dark blue shapes are sugar molecules, and you can see that this protein is covered in them!
If you haven’t already guessed — some sugars on the surface of coronavirus shells are similar to the sugars on human cell surfaces. There are numerous types of these )-⬣-⬣-⬣-⬣-⬣ chains. Check out this paper to see more about them:
Antibodies are another piece of this puzzle, and they are produced by the immune system to help stop intruders from harming the body. Humans produce antibodies to bind cells, viruses, and molecules. For example, antibodies are also produced against SARS-CoV-2, which helps us to directly fight the infection and COVID-19 disease.
Importantly, healthy humans also produce antibodies against any AB blood type that is not already present in their own body. For example, O blood types produce antibodies against sugar molecules to recognize A blood types as well as B blood types. Thus, A blood types will produce antibodies against sugar molecules to recognize B blood types.
This brings us back to the question: why are people with O blood type potentially at a reduced risk for infection by the SARS-CoV-2 coronavirus?
In fact, there are at least a few possible reasons for this:
- Perhaps coronavirus is able to bind sugar molecules on the surface of red blood cells in A blood type, and this helps the virus to infect human cells.
- Perhaps antibodies present in O blood type, against A and B blood type sugars, exhibit cross-reactivity with sugars on the surface of coronaviruses, and this may block the virus from infecting human cells.
- Perhaps the chains of sugars on the outer shell of coronaviruses are malformed when the virus replicates in O blood type, which is lacking the enzymes to link sugars, as in A and B blood types, and this makes hit harder for the virus to replicate or infect human cells.
One or more of the above scenarios are possible — and actually, there is evidence for all of them (see below)!
Read the following paper to learn more about possible sugar-binding sites on the outer surface of the coronavirus:
Read the following paper to learn more about antibodies against A blood type cross-reacting to block the interaction between the SARS-CoV-2 Spike protein and its human cell receptor:
Read the following paper to learn more about how coronaviruses (and other viruses) exploit host glycosylation for synthesis of the virus:
More evidence that risk may vary due to ABO blood types or sugars on the outer shell of coronavirus
Several studies demonstrate that sugar binding molecules like lectins and griffithsin prevent coronaviruses from reaching their viral target. Some also support that sugar binding sites exist on the outer shell of coronaviruses!
