Using a cellular model of adhesion, Guillon et al discovered that human anti–A antibodies inhibited interaction between angiotensin converting enzyme-2–dependent cellular adhesion to angiotensin converting enzyme-2–expressing cells. Further investigations discovered a protective effect of anti–A antibodies against intracellular uptake of SARS-CoV-1. One study, in particular, found that ABO polymorphism was associated with susceptibility to infection with SARS-CoV-1. Clinically, blood types have been linked to bacterial, parasitic, and viral infections, ,, ,,. On a molecular level, they can serve as receptors and coreceptors for pathogens and can also facilitate intracellular uptake of viral particles. Blood group antigens play a direct role in infection through various mechanisms. The most widely studied associations, however, have been in the realm of infectious diseases. īlood type has been identified as a risk factor in many disease processes, ranging from malignancy to venous and arterial thromboembolism. Recent studies have investigated blood type as a risk factor for COVID-19, ,, ,,. To date, multiple, population-based studies have discovered patient-level factors associated with worse outcomes after contracting COVID-19, including sex, race, ethnicity, age, obesity, and preexisting medical conditions, ,, ,, ,,. The importance of deciphering COVID-19–related risk factors has significant implications for triage and prognosis. Robust research efforts have been undertaken to determine risk factors for viral susceptibility and severe illness.

SARS-CoV-2 continued to spread through person-to-person transmission and swiftly escalated into a global emergency. In January 2020, the first case of COVID-19 was reported in the United States. Despite stringent measures to contain the viral outbreak, the illness continued to proliferate throughout China, overwhelming its hospitals resources and health care workers. From there, COVID-19 quickly spread throughout the Wuhan region. An outbreak of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) began as a cluster of patients developing pneumonia of unknown origin linked to a seafood market in the city of Wuhan. The COVID-19 pandemic began in December 2019.

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