Soon after the emergence of SARS-CoV-2, scientists embarked on a quest to uncover factors that could influence an individual’s susceptibility to infection and the severity of illness. Extensive studies conducted in China during 2020 suggested that individuals with blood type A might face a higher risk of infection, while those with blood type O could potentially possess a degree of protection. Although subsequent research yielded mixed results, public health experts remained uncertain about the significance of blood type as a potential risk factor for COVID-19.
Dr. Sean Stowell, an associate pathology professor at Brigham and Women’s Hospital and Harvard Medical School, collaborated with scientists from the U.S. Centers for Disease Control and Prevention to develop a blood-based test for COVID-19. During their research, Dr. Stowell made a critical observation. He discovered that the finger-like projections on the surface of the SARS-CoV-2 virus resembled the blood group proteins found on human cells. This connection held substantial importance as these viral projections, or proteins, facilitated the virus’s entry into and subsequent infection of human cells. If the virus recognized the blood group proteins, it indicated that certain blood types might enhance the virus’s ability to infect cells. This revelation offered a potential explanation for the role blood type could play in COVID-19 risk.
Together with his team, Dr. Stowell conducted a series of experiments to explore this connection further. The results, detailed in a recently published paper in the medical journal Blood, confirmed that cells from individuals with blood type A were indeed more susceptible to SARS-CoV-2 infection compared to cells from those with blood type O. Blood type O, characterized by minimal blood type proteins, acts as a universal donor that can be transfused to individuals with blood types A, B, or AB without triggering an immune response. On the other hand, blood types A, B, and AB each contain distinct groups of proteins, or antigens, which, as Dr. Stowell’s research elucidated, interact differently with the COVID-19 virus.
The studies demonstrated that individuals with blood type A faced an increased risk of infection ranging from 25% to 50%, depending on the specific variant involved. Notably, type A blood group cells were particularly vulnerable to Omicron variant viruses.
The heightened susceptibility of blood type A stems from SARS-CoV-2’s affinity for type A blood proteins. The virus possesses receptors that facilitate binding to cells with antigens from blood type A, making these cells more “sticky” for the virus, as Dr. Stowell explains. With a greater number of viruses attached to cells, the likelihood of finding the keyhole for infection, known as the ACE2 receptor, significantly increases. While blood group A doesn’t actively assist the virus in cell entry, it renders the cells stickier, making it easier for the virus to land on their surface. In individuals with type A blood, the abundance of A antigens enables the virus to attach to cell surfaces more readily than in individuals with type O blood.
Does this mean that individuals with blood type A should exercise exceptional caution to minimize exposure and face a higher risk of severe illness if infected? According to Dr. Stowell, it remains a possibility but is not definitive. Blood type represents only one of several factors that influence the risk of COVID-19 infection and the development of severe complications. While certain studies have documented a 48% increased risk of mortality from COVID-19 among individuals with type A blood, it’s important to note that not all individuals with type A blood exhibit the same quantity of A group antigens on their cells. Additionally, people possess varying levels of ACE2 receptors on their cells. Therefore, even individuals with type A blood may not necessarily face a higher risk of infection compared to those with type O blood. Consequently, there exists variability even among individuals with blood type A.
Conversely, Dr. Stowell cautions against assuming that individuals with blood type O possess immunity against COVID-19. Irrespective of blood type, individuals should continue to adopt proper precautions, including staying updated with vaccinations and wearing masks during periods of escalating infections. Dr. Stowell emphasizes the need for individuals to remain cautious and adhere to standard precautionary measures despite their blood group status.
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Practically, the newfound understanding of how blood types may influence COVID-19 risk could prove invaluable for healthcare professionals in effectively managing the risk among specific groups, such as the elderly and individuals with compromised immune systems. Although treatment approaches may not differ based on blood type, doctors can now exercise heightened vigilance in monitoring signs and symptoms of infection in elderly individuals or cancer patients with blood type A. Moreover, they can educate these patients about the importance of protecting themselves from exposure.
Dr. Stowell plans to expand on this research by investigating the implications of blood type B, which possesses antigens only slightly different from those found in type A, on COVID-19 risk. He expresses his team’s ongoing commitment to uncovering why the virus doesn’t bind to type B blood as effectively.