The blood group link was first announced by Chinese scientists in May last year. They hypothesized that blood group A (ABO system) may contribute to increased susceptibility to a new pathogen, while group O carriers are less susceptible to infection. The hypothesis of a relationship with the severity of COVID-19 was further confirmed by small studies in Italy and Spain, but Danish scientists found evidence of susceptibility to the virus depending on the blood group, but not the likelihood of complications. At the same time, observations from the United States did not confirm all of these conclusions.
To put an end to the scientific debate, researchers at the Intermountain Medical Center Heart Institute conducted a case-control study involving 108,000 confirmed COVID-19 patients. They analyzed the medical records that indicated the blood type. The range of clinical outcomes in patients was wide, from mild to the need for mechanical ventilation.
After adjusting the data for various factors, including gender, age, and blood Rh factor, the study authors found no relationship between blood type and susceptibility to infection and the severity of COVID-19. At the same time, the analysis confirmed the already well-known conclusions: the likelihood of complications is higher in men and in all patients over 60 years old, an additional risk factor is belonging to a non-white race and ethnic minorities.
The researchers suggested that previous evidence of blood type associations with coronavirus susceptibility and severity was due to small sample sizes, and many studies were retrospective and observational. Systematic errors and the influence of differences in the genetic background and geography of research are not excluded.
“Given the large-scale and promising nature of our study and the null results, we believe that associations of SARS-CoV-2 with blood groups are unlikely,” the study authors said.