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Type O- blood may have a protective effect against COVID-19

People who have type O and rhesus negative (Rh-) blood may have a slightly lower risk of infection with SARS-CoV-2 than those with other blood types, according to a recent study. On the opposite end of the spectrum, people with B+ blood were twice as likely to get infected compared to those with O-.

ABO status and COVID-19: what’s the connection?

The prevalence of various blood types in the population of the United States.

Researchers at the University of Toronto assessed the prevalence of SARS-CoV-2 infection, as well as the severity of COVID-19 illness or death of 225,556 patients who had their ABO blood group assessed between January 2007 and December 2019, and who were subsequently tested for SARS-CoV-2 between January 15 and June 30, 2020.

After accounting for common comorbidities (cardiac disease, chronic kidney disease, anemia, cancer, asthma, etc.), age, and other relevant characteristics, the researchers compiled an adjusted relative risk for each blood group.

According to the results, the O- blood group had a 2.1% risk of becoming infected with SARS-CoV-2, the lowest unadjusted probability out of all blood groups. The highest unadjusted probability of infection was 4.2% among the B+ blood group. There was also a lower risk for severe COVID-19 illness or death associated with type O blood group versus all others.

No safety in blood types

However, this doesn’t mean that people with O- blood are immune to the coronavirus — it’s just that they may be slightly less likely to get infected. As such, those with O- blood should still get vaccinated against COVID-19 and take all the necessary precautions.

The study also comes with its own limitations. For instance, the sample selected for this study was not random. It included only people who had their blood tested, and this non-randomness in sample selection tends to complicate the analysis and reduce the confidence in the results. The demographics also weren’t representative of the general population, with the mean age being 53.8 years and 29% of the participants being men.

But the sample size itself was adequate, numbering hundreds of thousands of participants, so people with O- blood may indeed have a favorable edge against the coronavirus. This fact is corroborated by other studies, such as research by Danish scientists who compared data from around 473,000 COVID-19–positive individuals with a control group of 2.2 million people in the general population, finding fewer infected people with blood type O and more people with A, B, and AB types.

Many other studies seem to have reported an association between type O blood and a reduced incidence of coronavirus infections. A study by researchers at Massachusetts General Hospital looking at patients in Italy and Spain found that blood type O had a 50% lower risk of severe coronavirus infection (i.e. needing intubation or supplemental oxygen) compared to patients with other blood types.  Another study from April 2020 found that among 1,559 coronavirus patients in New York City, a lower proportion than would be expected had Type O blood. And very early in the pandemic, a study of over 2,100 coronavirus patients in Wuhan and Shenzhen (not peer-reviewed) found that people with Type O blood had a lower risk of infection.

“Studies of the accuracy of serologic tests for anti-SARS-CoV-2 immunoglobulins may assess whether there is variation in antibody titers by ABO and Rh status,” the authors noted in the Annals of Internal Medicine. “Furthermore, among ongoing clinical trials of immunotherapy using convalescent plasma or of SARS-CoV-2 vaccines, the interaction between participant blood groups and therapeutic efficacy could be measured.”

People with blood type O may face lower risk of coronavirus infection or have milder symptoms

Two retrospective studies in Blood Advances add evidence for an association between blood type and COVID-19 risk, indicating that people with blood type O could be less susceptible to infection and experience milder disease. But this does not necessarily confirm causation. Further investigations on the mechanism of the different susceptibility to COVID-19 between blood group A and O individuals are needed and regardless of your blood type, you need to follow public health recommendations.

The first study from Denmark compared data from around 473,000 COVID-19–positive individuals with a control group of 2.2 million people in the general population, finding fewer infected people with blood type O and more people with A, B, and AB types. No associations were found between non-O blood groups and comorbidities that might explain infection rate differences.

The authors hypothesize that the presence of virus-neutralizing anti-A and anti-B antibodies on mucosal surfaces of some type O individuals may explain the relative protection for this blood type.

The second study from Vancouver, Canada on 95 critically ill COVID-19 patients in a hospital found that—after adjusting for sex, age, and comorbidities—patients with blood types A or AB were more likely to require mechanical ventilation than patients with types O or B (84% vs 61%, P = 0.02), indicating higher rates of lung damage.

Patients with blood types A and AB also had higher rates of dialysis for kidney failure, suggesting increased organ dysfunction or failure due to COVID-19 (32% vs 95%, P = 0.004). Patients with blood types A and AB did not have longer hospital stays than those with types O or B, but they did experience longer intensive care unit stays, which may signal greater COVID-19 severity.

A study in June looking at patients in Italy and Spain found that blood type O had a 50 percent reduced risk of severe coronavirus infection (i.e. needing intubation or supplemental oxygen) compared to patients with other blood types. A study published in July looking at patients in five major hospitals in the state of Massachusetts found that people with blood type O were less likely to test positive for COVID-19 than those with other blood types. Another study in April (pre-print and awaiting peer-review) found that among 1,559 coronavirus patients in New York City, a lower proportion than would be expected had Type O blood. Earlier in March, a study of over 2,100 coronavirus patients in Wuhan and Shenzhen (also not peer-reviewed) found that people with Type O blood had a lower risk of infection.

Past research analyzing a hospital outbreak in Hong Kong suggested that people with Type O blood were less susceptible to (the original, not the pandemic) SARS, which shares ~80 percent of its genetic code with the new coronavirus, SARS-CoV-2. A 2005 Clinical Microbiology Review also found that most individuals infected with SARS had non-O blood types. 

It’s important to emphasize that the type of reduction in risk achieved with appropriate physical distancing, wearing a mask, and hand hygiene are significantly better than depending on your blood group for protection, so people with blood type O should not be complacent about public health advice.

People with blood type A may be more vulnerable to COVID-19, study says

Chinese researchers took blood samples from more than 2,100 patients infected with the novel coronavirus in Wuhan and Shenzhen — two Chinese cities most affected by the COVID-19 pandemic.

After comparing the blood types with those of healthy populations, the researchers noticed that those with blood type A were more susceptible to infection and had a higher mortality rate than other blood types. In contrast, those with blood type O were less likely to get infected and when they did, they were less likely to have the disease progress into severe or critical stages that might kill them, compared to non-O blood types.

These findings applied to all genders and age groups. Although the results are preliminary, they warrant further investigation and might potentially have important clinical implications given the current crisis we’re experiencing.

“People of blood group A might need particularly strengthened personal protection to reduce the chance of infection,” wrote the research team led by Dr. Wang Xinghuan with the Centre for Evidence-Based and Translational Medicine at Zhongnan Hospital of Wuhan University and Dr. Jiao Zhao from the School Of Medicine at Shenzhen University of Science and Technology.

“Sars-CoV-2-infected patients with blood group A might need to receive more vigilant surveillance and aggressive treatment,” Wang wrote.

Blood is essentially made up of two types of blood cells (red and white), platelets, and a fluid called plasma. About half the blood (45%) is made up of blood cells, with the remaining 55% being plasma. Millions of blood cells are produced daily in the bone marrow, the soft spongy material that fills up bone cavities.

A person’s blood type is determined by proteins found on the surface of red blood cells called antigens. If antigen A is present in the red blood cells, then you have type A blood, while having B antigen present means you have type B blood. If both A and B are present, you have type AB blood. If neither antigen is present, you have type O blood.  

Blood types vary in a population according to ethnicity and ancestry. In the U.S., about 45% of the population is type O and 40% is type A. In Wuhan, which is the epicenter of the COVID-19 pandemic, about 32% of its 11 million inhabitants are type O and 34% are type A.

For 1,775 COVID-19 patients treated at Wuhan Jinyintan Hospital, the distribution was 25.8% type O and 37.7% type A. Similar ABO distribution patterns were observed in 398 other patients in two hospitals in Wuhan and Shenzhen.

When the researchers pooled the results, they found that of the 206 patients who had died because of complications related to COVID-19, 85 were blood type A (41.26% of registered deaths) and 52 were blood type O (about a quarter of the deaths). There were 63% more fatalities related to the novel coronavirus among individuals with blood type A compared to blood type O.

These are preliminary results, which were published in the preprint server medRxiv and haven’t been peer-reviewed. And although the sample size is over 2,000, it is dwarfed by the overall number of confirmed cases currently totaling over 200,000. The study is also purely observational and did not establish any mechanism between blood antigens and the coronavirus.

It wouldn’t be totally surprising that SARS-CoV-2, the coronavirus responsible for COVID-19, is blood type sensitive. The 2003 SARS outbreak caused by SARS-CoV-1, another coronavirus strain, also exhibited similar traits, in which individuals with blood type O were less susceptible to contracting the disease.

Another study published in 2005 found that anti-A antibodies inhibit the adhesion of SARS-CoV S protein-expressing cells.

If the findings hold scrutiny by other research groups, they might have important clinical implications. Individuals with blood type A might require more vigilant surveillance. Medical staff could also introduce ABO blood typing in their screening routine for SARS-CoV-2.

This being said, if you’re type A there’s no need to panic because it doesn’t mean you’ll be infected. Likewise, if your blood type is O, it doesn’t mean you’re absolutely safe, either. We should all continue to follow the guidelines set forth by the World Health Organization that call for social distancing and rigorous hand washing.

Credit: Pixabay.

What is the most common blood type?

Credit: Pixabay.

Credit: Pixabay.

Introduction

Without blood, the human body would simply stop working. This essential fluid of life dispenses crucial nutrients throughout the body, exchanges oxygen and carbon dioxide, and carries our immune system’s ‘militia’ to stave off infections. But not all blood is equal, and in the event of a transfusion, mixing incompatible blood types can lead to death.

Distribution of blood types

There are 4 main blood groups: A, B, AB and O, of which group O is the most common. In the United States, the average distribution of blood types is as follows:

  • O-positive: 38 percent
  • O-negative: 7 percent
  • A-positive: 34 percent
  • A-negative: 6 percent
  • B-positive: 9 percent
  • B-negative: 2 percent
  • AB-positive: 3 percent
  • AB-negative: 1 percent

blood type distribution

Different racial and ethnic groups typically see a different distribution. For instance, 45 percent of Caucasians are type O, but 51 percent of African-Americans and 57 percent of Hispanics are type O, according to the Red Cross. This Wikipedia page has the blood type distribution in every country.

Type O is the most demanded blood type in hospitals, both because it’s the most common and because O-negative blood is a universal donor type, meaning it is compatible with any blood type. Conversely, type AB-positive blood is called the universal recipient type because a person who has it can receive blood of any type.

How blood type is determined

Like eye color, blood type is genetically inherited from your parents. Whether your blood group is type A, B, AB or O is based on the blood types of your mother and father. For instance, if your mum is AB and your dad is A, you can expect to be A, B, or AB. If mum is AB and dad is O, the child will have an A or B blood type. When both parents are A, the child will have either O or A.

Credit: Red Cross.

Credit: Red Cross.

Blood is essentially made up of two types of blood cells (red and white), platelets, and a fluid called plasma. About half the blood (45%) is made up of blood cells, with the remaining 55% being plasma. Millions of blood cells are produced daily in the bone marrow, the soft spongy material that fills up bone cavities.

A person’s blood type is determined by proteins found on the surface of red blood cells called antigens. If antigen A is present in the red blood cells, then you have type A blood, while having B antigen present means you have type B blood. If both A and B are present, you have type AB blood. If neither antigen is present, you have type O blood.  

Besides the ABO classification, there’s also another blood type grouping that involves Rhesus (Rh) factors. The name comes from the Rhesus monkeys, in which such proteins were first discovered. Rhesus factor D, which is the most important, is present in 85% of people, making them Rhesus positive. The remaining 15% are grouped Rhesus negative. The Rh grouping can be very important in some situations. For instance, a baby’s life can be endangered if it inherits a Rhesus positive blood type from the father while the mother is Rhesus negative — in such a situation, the mother can form antibodies against her own baby’s blood.

Blood groupings and transfusions

Credit: Red Cross.

In order to safely perform a blood transfusion, it’s essential that a patient receives a blood type that is compatible with their own. If the blood type is incompatible, the red blood cells can clump together, producing clots that block blood vessels and cause death. Generally, for the ABO grouping, blood transfusions follow these rules:

  • A person with type A can donate to a person with type A or AB.
  • A person with type B blood can donate to a person with type B or AB.
  • A person with AB type blood can only donate to a person with AB. However, a person with blood type AB can receive blood from anyone, being the universal recipient.
  • A person with O type blood can donate to anyone, being the universal donor. This is because type O blood has no antigen on the surface of its red blood cells. However, people with type O blood can only receive type O.

People with Rh-positive blood can receive either positive or negative donations but those who have Rh-negative blood can only receive other Rh negative blood.

Doctors will test your blood before you are allowed to donate or receive blood. However, in the event of an emergency when the patient’s blood type is unknown, type O blood will be used.

It’s important to note that there are more than 600 other known antigens, the presence or absence of which creates “rare blood types.” The ABO grouping works just fine for most people, but in some rare cases, certain blood types may be unique to specific ethnic or racial groups. For instance, many patients with sickle cell disease require an African-American blood donation. That’s why it’s still ideal to match a blood donation type to its recipient exactly, accounting for both antigen types and Rh factor.