(Vienna, 06 August 2026) Since the start of the COVID-19 pandemic, scientific research has been investigating whether blood group influences the risk of SARS-CoV-2 infection, the immune response following vaccination, or the course of the disease. Whilst several studies have described associations with the risk of infection, the findings regarding the vaccine response and disease severity have remained contradictory. A study led by the Medical University of Vienna now shows that neither the ABO blood group nor the Rhesus factor influences the antibody response following a SARS-CoV-2 booster vaccination or the severity of COVID-19. However, differences were found in the incidence of so-called breakthrough infections – that is, infections despite being fully vaccinated. The study results were published in the journal "Influenza and Other Respiratory Viruses".
For the study, the research team led by Daniela Sieghart and Helga Radner (Division of Rheumatology, Department of Medicine III, MedUni Vienna) analysed data from 3,066 adults who had received a booster dose of an mRNA vaccine following their primary COVID-19 vaccination. The researchers examined both the antibody response four weeks after vaccination and the occurrence of SARS-CoV-2 breakthrough infections and their clinical course over a period of six months. They measured antibodies against the receptor-binding domain (RBD) of the spike protein – the part of the virus that enables SARS-CoV-2 to bind to human cells – as well as neutralising antibodies in a subgroup. These can directly prevent the virus from infecting cells.
The analyses revealed no differences in the antibody response between the individual ABO blood groups or between Rhesus-positive and Rhesus-negative individuals. The concentrations of neutralising antibodies against the original virus strain and the Omicron variant were also comparable. The study therefore provides no evidence that blood group influences the immune response following a COVID-19 booster vaccination.
The picture was different for breakthrough infections: within six months of the booster vaccination, these occurred in 35.6 per cent of participants. Whilst 37.7 per cent of people with blood group A and 36.7 per cent with blood group O had a breakthrough infection, the figures were 30 per cent for blood group B and 28 per cent for blood group AB. After taking other influencing factors into account, a lower risk remained, particularly for blood group AB. In contrast, no association was found between the Rhesus factor and the risk of infection. The researchers also found no differences between blood groups or the Rhesus factor in terms of disease severity. In the cohort studied, all cases of COVID-19 ranged from asymptomatic to moderate; no severe cases requiring hospitalisation were observed.
"Our findings suggest that, whilst the ABO blood group may be associated with the risk of viral transmission or breakthrough infection, it is not associated with the vaccine’s efficacy in terms of antibody production or with the severity of COVID-19," summarises first author Daniela Sieghart. However, according to the researchers, the underlying biological mechanisms remain not fully understood.
Publication: Influenza and Other Respiratory Viruses
Impact of ABO Blood System on Immunogenicity and Vaccine Efficacy of COVID-19 Booster Vaccination - A Population-Based Study of 3066 Individuals.
Daniela Sieghart, Galateja Jordakieva, Caroline Dürrschmid, Claudia A. Hana, Lan Vi Tran, Leonhard X. Heinz, Helmuth Haslacher, Markus Zlesak, Valentin Marzoner, Philip Nasztl, Giulia Piccini, Alessandro Manenti, Emanuele Montomoli, Anselm Jorda, Clemens Fedrizzi, Timothy Hasenoehrl, Andrej Zdravkovic, Karolina Anderle, Ursula Wiedermann, Susanne Drapalik, Helmut Steinbrecher, Felix Bergmann, Christa Firbas, Barbara Wagner, Margherita Leonardi, Giulio Pierleoni, Matilde Ballini, Linda Benincasa, Serena Marchi, Claudia Maria Trombetta, Thomas Perkmann, Richard Crevenna, Markus Zeitlinger, Michael Bonelli, Daniel Aletaha#, Helga Radner.
DOI: 10.1111/irv.70.300