Study population and setting
This was an unmatched case-control study, in which ABO-typed blood samples were collected from infected hospital cases, and ABO blood group distribution was captured from recent surveys of “normal people” to serve as comparison controls. Cases were included from three hospitals in Wuhan, Hubei province and Shenzhen, Guangdong province, China. No specific time period was provided for when cases were infected or selected, and information was not provided on controls. There were a total of 1775 patients infected with SARS-CoV-2 (COVID-19 cases), including 206 deaths, from the Jinyintan Hospital in Wuhan. An additional 113 COVID-19 cases were included from Renmin Hospital of Wuhan University, and 285 COVID-19 cases from Shenzhen Third People’s Hospital. There were a total of 3694 controls from Wuhan City and 23386 controls from Shenzhen City.
Summary of Main Findings
Blood group A was associated with an increased risk for COVID-19, whereas blood group O was associated with a decreased risk, suggesting that the ABO blood type is a biomarker for differential susceptibility to COVID-19.
There are few studies that have examined differential susceptibility to SARS-CoV-2 infection; ultimately this study assesses susceptibility to COVID-19 (disease status, not infection), but generates future hypotheses for testing around blood type and infection, as well as further analyses of progression to disease. While multivariable analyses were not possible and therefore the role of chronic medical conditions is still unclear, this study made use of existing hospital data and surveys in order to do a rapid and methodologically replicable examination of a potential biomarker for COVID-19 susceptibility.
The control group appears to have been sampled years before the study, is from a different source population and appears to have differences in at least age composition from the target population. Further, because controls are historical, we do not know if they ultimately were infected during the time period of this study.
This is one of the first studies of risk factors for COVID-19 susceptibility. This has potential implications for future prevention efforts (e.g. biomarker for who might need extra protection or who may need to take extra precautions against infection), however underlying methodological issues suggest caution in terms of interpretation. Importantly, a biological mechanism was hypothesized, though it requires further assessment. Ongoing and future serological studies with case reporting ascertainment may also consider assessment of blood type.