Revisiting the Association of ABO Blood Groups Alongside Vaccination With Patient Outcomes in SARS‐CoV‐2 Respiratory Infection: A Prospective Observational Cohort Study in Bristol, UK 2020–2023

ABSTRACT Background The 2023 SARS‐CoV‐2 environment differs greatly from the initial outbreak, with new variants and widespread vaccination. Early in the pandemic, blood group A was linked to increased hospitalisation and poor outcomes, but its role now, since the availability of vaccination, is unclear. Methods We analysed data (1 August 2020–31 July 2023) from a prospective cohort of adults hospitalised in Bristol with SARS‐CoV‐2 and known ABO group ( n = 3413). Admission date acted as a proxy for viral strain. Regression models assessed length of stay, survival, cardiovascular complications and ICU admission in non‐O groups versus Group O. Results Group A was over‐represented and Group O was under‐represented, compared to the blood donor population, except during Alpha dominance ( p < 0.001; Alpha: p = 0.796). ABO group generally did not affect cardiovascular risk. However, during Wild‐Type, Group AB had higher odds of cardiovascular complications (odds ratio [OR] = 3.18, p = 0.060) and intensive care unit [ICU] admission (OR = 4.79, p = 0.013). During Omicron, AB group patients had lower 30‐day survival (HR = 2.09, p = 0.018). Group A was less likely to be discharged during Alpha (HR = 0.85, p = 0.013), while Group B was more likely to be discharged during Omicron (HR = 1.30, p = 0.002). Conclusions ABO groups may still influence hospitalisation risk but appear less relevant to outcomes once admitted, likely reflecting advances in care and vaccination.