By Brian Rose
Which blood type is more susceptible to coronavirus? The novel Coronavirus disease 2019 (COVID-19) has been spreading worldwide since the end of 2019. The condition seems to hit harder with severe symptoms in some individuals, while others show mild symptoms. The mortality rate of COVID-19 is also variable in different regions of the world. Scientists thought it to be due to the age factor or due to underlying medical conditions. But it is also seen that young adults with no history of previous medical illness were showing severe symptoms and needing ventilatory support to cope with the virus. Many research studies were done to know the links between certain risk factors and the severity of the disease. Some of these studies revealed that there is a link between blood type and susceptibility to coronavirus. There are also many past research studies and connections with the blood type or group such as stomach flu.
Factors Controlling the Severity of COVID-19 Infection
There was too little information about coronavirus infectivity before it emerged in the Chinese province of Wuhan in late 2019. After its emergence, scientists and researchers started to study the virus structure, its transmission, causative mechanism, diagnosis, how to control its spread, and its management. The virus is linked to the class of SARS virus hence named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The virus causes respiratory illness, which can progress to pneumonia or acute respiratory distress. The symptoms in different infected patients vary in severity. Some patients show mild illness with fever, myalgias, cough, and sore throat. While others may show severe symptoms with shortness of breath and not maintaining oxygen saturation. These may require ventilatory support. The mild cases resolve without any treatment or care by self-isolating within 14 days. But the cases with severe symptoms may need hospitalization and intensive care. Many people land in the hospital ER with severe shortness of breath and with complications. Some of these serious patients recover with urgent necessary care (intubation, ventilatory support) while others die coping up with the disease. So, this COVID-19 infection varies in symptoms and presentation. It depends on various factors because no single factor can be responsible for so many varying presentations.
Studies have shown many factors responsible for disease severity, including age, immune status, underlying diseases, genetic factors, obesity, smoking, and blood type. The risk of infection and mortality rate is higher in those who are elderly and have an underlying condition. For example, diabetes and heart diseases exacerbate the symptoms of COVID-19, increasing the chances of hospitalization. These patients have a higher mortality risk as compared to those patients without these underlying conditions. Similarly, genetics also have shown to play a role in susceptibility to COVID-19 infectivity. A study published in April 2020 in the Journal of Virology suggested that specific combinations of HLA genes (human leukocyte antigen) may be protective against COVID-19 while other combinations make a person more vulnerable to getting infected with a coronavirus. HLA genes are responsible for immune system regulation and making immune cells recognize the invading foreign organisms and combat them. In another study, it is suggested that genes responsible for building ACE2 (angiotensin-converting enzyme 2) receptors differ in those with severe symptoms of COVID-19 from those showing mild or no symptoms.
Role of Blood Type O in COVID-19
Blood type is another common factor that determines the individual’s susceptibility to contracting SARS-CoV-2. Studies show that ABO blood group systems have some connections with the risk of having COVID-19. Various studies concluded that people with blood type O are less susceptible to getting COVID-19, while those with blood type A have higher chances of getting COVID-19. The idea that blood type can affect vulnerability to infections is not new, as, in the past, researchers have shown that it does affect the risk of getting infected. A senior expert of infectious disease at John Hopkins Centre for Health Security, Amesh A. Adalja, said ‘’blood type could sometimes be linked to susceptibility to various infectious diseases.’’ However, genetics also plays a role in determining vulnerability. The links of blood type with certain infections can be seen in those with Sickle Cell Diseases, and the affected people are resistant to malaria. Research about stomach flu found that people with blood type O are at high risk of getting infected with norovirus (causative organism of stomach flu). Blood type O also reduces the chances of getting a stroke, heart disease, and cognitive impairments. There are various studies available on these correlations between blood type O and illnesses.
Blood type is determined by genetics, and different blood types have different features that make every type unique. Every blood type differs in antigens and antibodies present on their surface. These are essential determinants for assessing the severity and susceptibility of diseases in relation to blood types.
Studies Showing Blood Type O as a Protective Factor Against COVID-19
Since the beginning of COVID, pandemic scientists and researchers worldwide have been trying to find the probable factors and risks associated with COVID-19 severity. They are also busy finding the definitive treatment and vaccine for the disease. Various studies are done in different regions of the world to find out the link between blood type and COVID-19. The studies suggest that people with blood type O have reduced chances of getting infected as compared with other blood types. To get a better insight, we will discuss various studies showing the relation between blood type O and coronavirus infection.
A study is conducted by researchers from the Southern University of Science and Technology, Shenzhen, China, in collaboration with colleagues from other institutions. The study aimed at assessing the correlation between blood type and hospitalization due to COVID-19. In this study, researchers analyzed the blood type of 2,173 COVID-positive patients that were hospitalized and received care in three hospitals in Wuhan and Shenzhen. The blood type distribution among these patients was then compared with the distribution among the general population in those specific regions. The findings of this study are:
● Blood type A is present in 31% of the normal population as compared to 38% in COVID-positive patients.
● 24% of people among the general population have blood type B, while 26% of COVID-positive patients have blood type B.
● Blood type AB is present in 9% of the general population, while 10% of hospitalized patients have an AB blood type.
● 34% of the general population has blood type O, while 25% of hospitalized COVID-positive patients have blood type O.
These results concluded that blood type A has higher chances of COVID-19 infection as compared to other blood types. People with blood type O have a significantly lower risk of getting infected. This study was published on Medrxiv on 27 March 2020.
Another study conducted in New York was published on 11 April 2020 on Medrxiv. In this study, scientists looked at 1,559 people in Newyork Presbyterian hospitals who were tested for COVID-19. Out of these, 682 people were tested to be COVID-19 positive. Analyzing the blood types suggested a 33% increased risk of people with blood type A being COVID-19 positive compared to non-A group types. The study also concludes that individuals with O blood type (both O+ve and O-ve) were less likely to test positive for COVID-19.
These statistics also suggested that blood type O somehow is a protective factor against COVID-19 infection.
How Blood Type O is Protective Against COVID-19?
The studies have shown the protective role of blood type O, but the mechanism behind it is still not clear. More studies are on the go to find evidence that what makes blood type O a protective factor against coronavirus. But until now, there is some evidence from past studies and on the basis of recent studies. Blood type is determined by the presence of sugar molecules with certain proteins or lipids on the surface of red blood cells. These are called antigens. Blood type A has A antigen, blood type B has B antigens, AB has A and B antigens, O has no antigens. Apart from these antigens, the blood types also have antibodies on their surface due to which it is necessary to transfuse the blood type of the same group. A blood type has anti-b antibodies, B blood type has anti-A antibodies, AB has no antibodies as it contains both antigens, and O blood type has both A and B antibodies. The antibodies attack all the antigens which are not present on their surface. For instance, blood type A has anti-b antibodies which will attack the B antigen. Similarly, people with blood type B have antibodies for A antigens. AB blood type has no antibodies, and blood type O has both antibodies against A and B antigens.
Coronavirus is known to have a similar antigen on its surface as an ABO blood type. Naturally occurring antibodies against A and B antigens in blood type O will inhibit the binding of the virus to the host cell. It will minimize the severity of the disease. Another theory suggests that coronavirus replicates in the human cells that are responsible for expressing blood antigens. Hence the viral particles are coated in the infected person’s blood antigens. It simply means that when an infected person with blood type A transmits the virus to a person with blood type O, they have the antibodies to fight with the virus (because they have antigens coated on the surface). Another study suggests that the binding of SARS-CoV-2 in human cells necessary for infecting is inhibited by anti-A antibodies, which are present in people with blood type O. SARS-CoV-2 has spike proteins, which are attached to the host cells ACE2 receptors (angiotensin-converting enzyme 2) in the lungs. The virus is able to infect and replicate after the attachment. According to the study anti-A, the antibody inhibits this attachment, thereby preventing the cells from getting infected with the virus. People with blood type O naturally have anti-A antibodies that protect them from viral (COVID-19) infection. Genetics also plays a role in all these blood types and ACE2 receptors. It is seen that the genes coding for ACE2 receptors also differs in patients with severe symptomatic disease and those with mild symptoms. Since these receptors are present in the lungs, and once the virus infects the lungs, the disease can worsen, so inhibiting its attachment also stops the disease progression towards complications.
So collectively, genetics and blood type play a combined role in determining a person’s susceptibility for COVID-19 infections. Various factors other than these also increase or decrease vulnerability to the severity of symptoms. We cannot say that blood type O provides 100% protection against COVID-19. But having blood type O can lower your risk of contracting the virus. And if you get infected, you may have mild to no symptoms if you have blood type O. Studies are still going, and it’ll take some more time to have some solid proof and results in favor of this. But there is definitely a link between blood type and severity of COVID-19 infections because the past studies also supported this statement.
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