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Best Evidence Topic report: does blood group type O decrease the risk of severe COVID-19 infection?
  1. Mostafa Alavi-Moghaddam1,
  2. Zohreh Tajabadi2,
  3. Sogand Najafpour3
  1. 1 Emergency Medicine Department, Imam Hossein Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran
  2. 2 Digestive Disease Research Institute, Tehran Universiy of Medical Sciences, Tehran, Iran
  3. 3 Shahid Beheshti University of Medical Sciences, Tehran, Iran
  1. Correspondence to Dr Mostafa Alavi-Moghaddam, Emergency Medicine, Shahid Beheshti University of Medical Sciences, Tehran, 1617763141, Iran; mosalavi{at}


A short-cut systematic review was conducted using a described protocol. The three-part question addressed was: In patients with COVID-19 infection, does blood group type O versus non-O blood groups lead to a lower risk of severe COVID-19 infection? MEDLINE, Embase, and Cochrane databases were searched for relevant evidence. Altogether, 238 papers were found using the search strategy developed. Seventeen provided the best evidence to answer the three-part question. The data on first author name, publication year, country of origin, study type, study sample size, participant’s gender, reported effect sizes, main findings and limitations were extracted from the relevant studies and listed in a table. Finally, 4 out of 17 studies revealed that having blood group type O may be associated with a lower risk of severe COVID-19 among patients with COVID-19 infection and the 13 remaining studies reported no significant relationship between having O blood group and risk of COVID-19 severity among the infected individuals. Of three systematic reviews and meta-analyses identified, none detected a protective effect of blood group type O. The clinical bottom line is that the best available evidence does not support the notion that blood group type O is protective against serious outcomes in COVID-19.

  • COVID-19
  • triage
  • acute medicine
  • acute care

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  • Handling editor Richard Body

  • Contributors MA-M contributed to planning, designing and determining the conception. ZT and SN contributed to conducting and reporting of the work. ZT contributed to acquisition of data. MA-M and ZT contributed to interpretation of data.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; internally peer reviewed.