Question: I remember hearing a long time ago (at least a long time ago in COVID) that blood type might be associated with disease severity.  And that O blood type might be protective.  This stuck in my mind because I have O blood type and I admit, the news felt slightly reassuring.  Is it true?  Any updates?

Answer: I remember that too!  In fact, our Q&A from 6/23/20 gives a good overview of what we knew 1+ years ago.  There has been a lot of work since then, but the additional science has made the picture murkier.  We don’t know whether any given blood type is protective against infection or disease severity.  Here’s a quick list of competing findings, much of which I’ve drawn from a literature review published last month, which also describes the strengths/limitations of these studies:

• Findings support blood type correlation with infection and/or disease severity.
  • Barnkob et. al. find that O-type blood is associated with decreased risk of infection, but  no difference between ABO blood type and progression of illness to hospitalization or mortality.  O-type protective against infection.
  • Latz et. al. find that O-type blood is associated with decreased risk of infection, and find no association between blood type and disease severity.  O-type protective against infection.
  • Li et. al. find that O-type blood is associated with decreased risk of infection and A-type blood is associated with increased risk of infection, and there is no association between blood type and disease severity.  O-type protective against infection.
  • Rey et. al. find that O-type blood is associated with decreased odds of infection and of disease severity as compared with non-O-type blood. O-type protective against infection and death.
  • Zhao et. al.  find that A-type blood is associated with increased risk of infection and death as compared with non-A type blood, while O-type blood is associated with decreased risk of infection and death as compared with non-O type blood. O-type protective against infection and death.
  • Zietz et. al. find that A-type blood and B-type blood is associated with increased risk of infection as compared with O-type blood. A-type blood was also associated with decreased risk of intubation and death. Rh-positive is associated with increased risk of infection, intubation, and death as compared with Rh-negative. O-type protective against infection and death. A-type protective against death.
  • Hoiland et. al. find that A-type and AB-type blood is associated with increased risk of ventilation and prolonged ICU stay as compared with O-type and B-type blood, however, no differences in mortality were observed by blood type. O-type and B-type protective against ventilation and ICU stay.
  • Goker et. al. find that A-type blood is associated with increased risk of infection. No differences in disease severity by blood type were observed. O-type protective against infection. 
  • Bennet et. al.  find that AB-type blood is associated with decreased risk of intubation and death.  AB-type protective against intubation and death.
  • Almahdi et. al. find that AB-type blood is associated with decreased risk of infection and B-type is associated with increased risk of infection. No association between blood type and disease severity was identified. AB-type protective against infection.
• Findings do NOT support blood type correlation with infection and/or disease severity.
  • Barnkob et. al. find that O-type blood is associated with decreased risk of infection, but  no difference between ABO blood type and progression of illness to hospitalization or mortality. No association between blood type and disease severity.
  • Latz et. al. find that O-type blood is associated with decreased risk of infection, and find no association between blood type and disease severity.
  • Li et. al. find that O-type blood is associated with decreased risk of infection and A-type blood is associated with increased risk of infection, and there is no association between blood type and disease severity.
  • Leaf et. al. find no association between blood type and death, though A-type blood may increase risk of disease severity and O-type may decrease risk of disease severity among Whites. No association between blood type and mortality.
  • Boudin et. al. find no association between blood type and infection risk or disease severity. 
  • Goker et. al. find that A-type blood is associated with increased risk of infection. No differences in disease severity by blood type were observed.  No association between blood type and disease severity.
  • Hoiland et. al. find that A-type and AB-type blood is associated with increased risk of ventilation and prolonged ICU stay as compared with O-type and B-type blood, however, no differences in mortality were observed by blood type. No association between blood type and mortality.
  • Almahdi et. al. find that AB-type blood is associated with decreased risk of infection and B-type is associated with increased risk of infection. No association between blood type and disease severity was identified. No association between blood type and disease severity.
  • Anderson et. al. find no association between blood type and infection risk or disease severity.