Blood Type and COVID: Infection Risk and Severity

By Dr. Brandon Colby MD, a medical expert specializing in personalized preventive medicine and clinical genomics.

Research into the relationship between blood type and COVID-19 has contributed meaningfully to our understanding of who may be at higher risk of infection and severe outcomes. This article summarizes the key findings published to date.

Overview of Blood Type and COVID Research

Research published in Blood Advances on October 14, 2020 found that people with blood type O may be less likely to become infected with COVID-19, while those with blood types A and AB may be at increased risk of suffering from severe coronavirus-related illness.

In addition to individuals with blood type O having a lower risk of infection, the studies also found outcomes were less severe compared to people with other blood types.

Type O Blood Group

In a retrospective study, researchers examined Danish health registry data from over 473,000 people tested for COVID-19 in Denmark, comparing them to over 2.2 million people from the general population. Out of all positive results, fewer people were in blood group O and more were in types A, B, and AB. This suggests people with blood types A, B, and AB may have increased COVID-19 susceptibility. The researchers also examined ethnic subgroups and concluded that fewer people in all ethnicities with blood type O tested positive.

Blood Groups A and AB

In a separate study of 95 COVID-19 patients in Vancouver, Canada, those with blood type A and AB exhibited greater COVID-19 severity compared to types B and O. These patients suffered severe COVID-19-related complications requiring mechanical ventilation and were at higher risk of lung injury, kidney failure, and conditions including blood clots, strokes, and deep vein thrombosis. Days spent in hospital were similar across blood type groups despite the greater severity of illness in A and AB patients.

Why There May Be a Connection Between Blood Type and COVID-19

Blood type is determined by the presence or absence of A and B antigens on red blood cells. Type A has an A antigen and a B antibody in plasma. Type B has a B antigen and an A antibody in plasma. Type AB has both the A and B antigens. Type O has neither A nor B antigens on red cells but has both antibodies in plasma. Many experts suspect people with Type O blood may have an immune system better equipped to fight viruses because of the A and B antibodies.

How Genes Play a Role in Blood Type and COVID

A genome-wide association study published in the New England Journal of Medicine, analyzing data from populations including Wuhan, China, confirmed that blood group O is associated with a lower risk of acquiring COVID-19 compared to non-O blood groups, while blood group A is associated with a higher risk than non-A blood groups.

The study found genetic variants in two areas of the human genome associated with increased risk of severe COVID-19 complications. One cluster on chromosome 3 covers six genes with relevant functions, encoding a transporter protein that interacts with the ACE2 receptor (the surface receptor through which the virus binds to and infects human cells) and plays a role in immune response in the lungs' airways. Chromosome 9, which determines blood type, was also an area of interest. Researchers found a genetic variant associated with increased levels of interleukin-6, which affects inflammation in the body.

In the study, individuals in blood group A were around 50% more likely to need oxygen support or a ventilator if they tested positive for coronavirus, based on populations from Italy and Spain undergoing treatment for severe COVID-19.

Disputing the ABO Blood Group and COVID Connection

Not all researchers have reached the same conclusions. Harvard Medical School researchers at Mass General studied 1,289 symptomatic adult patients who tested positive and found no significant correlations between ABO blood type and SARS-CoV-2 infection. Their statistical analysis found no independent effect of blood type on intubation or death.

Ang Li, MD, an assistant professor of hematology and oncology at Baylor College of Medicine, has noted that the limitation of some studies is that they compare all COVID patients versus all non-COVID patients, rather than severe versus non-severe cases, making it difficult to distinguish between susceptibility and severity effects.

Hematology researchers continue to study this relationship. Some studies have suggested risk factors such as obesity, age, and pre-existing conditions may also increase disease severity, though people without these factors have also experienced severe outcomes.

How to Find Out Your Blood Type

Knowing your blood type is useful for several reasons. In an emergency requiring a blood transfusion, healthcare professionals need to know your blood type immediately. You may also want to consider donating blood if your type is in high demand. Blood type also relates to a range of health considerations including risks for certain cardiovascular conditions.

If you have already taken a DNA test from 23andMe, AncestryDNA, or MyHeritage, you can download your raw data and upload it to Sequencing for a blood type analysis. If you have not yet taken a DNA test, Sequencing offers whole genome sequencing and other tests that can be used to determine blood type along with a wide range of other health insights.

About the Author

Dr. Brandon Colby MD is a US physician specializing in the personalized prevention of disease through the use of genomic technologies. He is an expert in genetic testing, genetic analysis, and precision medicine. Dr. Colby is the founder of Sequencing and the author of Outsmart Your Genes.

Dr. Colby holds an MD from the Mount Sinai School of Medicine, an MBA from Stanford University's Graduate School of Business, and a degree in Genetics with Honors from the University of Michigan. He is an Affiliate Specialist of the American College of Medical Genetics and Genomics (ACMG), an Associate of the American College of Preventive Medicine (ACPM), and a member of the National Society of Genetic Counselors (NSGC).