[UNSUBSTANTIATED] Do studies prove that infectivity and severity of COVID-19 are correlated with blood types?

Screenshot of the Facebook post.

The Claim and Our Verdict

• The claim: A Facebook post published June 7, 2021, claims that some studies conducted in various countries have found the susceptibility and hospitalization rate of COVID-19 were correlated with blood type.
• Fact-checking:
  • The papers cited in the claim show that there may be a correlation between blood type and COVID-19 susceptibility but fail to prove the relationship between blood type and hospitalization from COVID-19. The biological mechanism behind this association has only been hypothesised, but not rigorously demonstrated. The more robust association and its underlying mechanisms and factors need to be further investigated. They also suggest that the associations between non-O blood types and susceptibility to COVID-19 do not explain the apparent protection enjoyed by individuals with the blood type O.
  • Further keyword searches found more studies discussing this topic. It was found that widespread interest in blood types as potential risk factors has provoked controversy and disagreement in academia. Based on the available information, different studies have contrasting conclusions and have yet to reach agreement on this topic.
• Our ruling: Therefore, we rate the claim as UNSUBSTANTIATED.

News Brief

A Facebook post published June 7, 2021 claims that some studies undertaken in various countries have found a correlation between the infectivity and severity of COVID-19 and ABO blood types. The blood type O has higher protection against COVID-19, while the blood type A has a higher rate of infection and hospitalization. The claim attached a hyperlink of an article from UrbanLifeHK, in which several scientific papers were cited.

As of the issuance of this report, it had been shared 45 times and had received 6 comments and 172 like or reactions.

Fact-checking

The findings of the three papers cited in the claim could be summarized as follows:

The first paper was published on July 15, 2021, in the journal of Clinical Infectious Diseases, titled as “relationship between the ABO blood group and the Coronavirus Disease 2019(COVID-19).” The study collected ABO-typed blood samples from 1,775 patients infected with COVID-19 and 206 deceased cases at the Jinyintan Hospital in Wuhan, China. Another 113 and 285 patients with COVID-19 were respectively recruited from Renmin Hospital of Wuhan University, Hubei province, and Shenzhen Third People’s Hospital, Guangdong province, China. Two recent surveys of ABO blood type distribution of 3694 non-COVID-19 people from Wuhan City, and 23386 non-COVID-19 people from Shenzhen City were used as comparison controls for the Wuhan and Shenzhen patients with COVID-19, respectively. The study found that blood type A was associated with an increased risk, whereas blood type O was associated with a decreased risk. It indicates that the difference in susceptibility to COVID-19 between blood type O and blood type A could be linked to the presence of natural anti-blood type antibodies, particularly anti-A antibody, in the blood. This hypothesis will need direct studies to prove. There may also be other mechanisms underlying the ABO blood type-differentiated susceptibility for COVID-19 that require further studies to elucidate. Other factors, such as chronic diseases that could potentially affect the chance and severity of COVID-19 infection were not addressed in the present study due to insufficient information, which limits the significance of the study.

The second paper was published on Oct. 27, 2020, in the journal Blood Advances, titled as “Reduced prevalence of SARS-CoV-2 infection in ABO blood type O.” The study conducted a retrospective cohort analysis of 473,654 individuals with registered blood type information. They were tested for COVID-19 between February 27 and July 30, 2020. A reference group with relevant blood type information from 2,204,742 non-tested individuals was included. It also demonstrates that blood type O is significantly associated with reduced susceptibility to COVID-19. It postulated several hypotheses to explain the results. In vitro studies have indicated that SARS-CoV-1 (a strain of coronavirus that causes severe acute respiratory syndrome [SARS)]) particles can be glycosylated by the A variant of the ABO glycosyltransferases, allowing anti-A antibodies to neutralize the virus. Although not studied, it is likely to be the case for the B variant, as well, and, therefore, for anti-B antibodies. Since anti-A and anti-B are present on mucosal surfaces in some individuals lacking the corresponding ABO blood type, this might explain the relative protection of blood type O individuals. Alternatively, the effect could be indirect, as a result of the association between ABO blood types and levels of von Willebrand factor, which is higher in non-O individuals and who are also more prone to arterial and venous thrombosis, which are important comorbidities for COVID-19. Therefore, the causal relationship between blood type O and its reduced risk was based on several hypotheses. It does not lead to a solid conclusion. The paper also highlights that this study does not identify ABO blood type as a risk factor for hospitalization or death from COVID-19, nor does it explain the apparent protection enjoyed by type O individuals.

The third paper was published on June 17, 2020, in The New England Journal of Medicine, titled as “Genomewide association study of severe COVID-19 with respiratory failure.” The genomewide association study involved 835 patients and 1,255 control participants from Italy, and 775 patients and 950 control participants from Spain. The study found a lower risk for blood type O to acquire COVID-19 and a higher risk of getting COVID-19 associated with blood type A. The biological mechanisms underlying these findings may have to do with the ABO blood types, such as the development of neutralizing antibodies against protein-linked N-glycans and other biologic effects of the identified variant including the stabilization of von Wille- brand factor. The study also emphasised the necessity of further exploration of current findings, both as to understand their usefulness in clinical risk management and towards a mechanistic understanding of the underlying pathological mechanisms.

The above findings demonstrate that the three papers prove blood types only have a possible association with the susceptibility to COVID-19 and have no connection with hospitalisation and deaths due to COVID-19. The biological mechanism underlying this association has not been rigorously proven but has only been hypothesised. Further study is needed to better understand the association and underlying biological mechanisms. Based on the findings of the above research, it cannot be concluded that blood type O population has a higher protection against COVID-19.

Further keyword searches found the following relevant studies.

A paper was published on July 12, 2020, in the journal of Annals of Haematology, entitled “Blood type and outcomes in patients with COVID-19.” It has drawn a different conclusion. The study collected and analysed data of patients (excluding those under 18 years old) who received a COVID-19 test performed between March 6 and April 16, 2020, from five major hospitals in Massachusetts, USA. Hospitalization, intubation, and death were evaluated for association with blood type. Based on the results, the study concludes that blood type is not associated with risk of progression to severe disease requiring intubation or causing death. According to the study, patients with blood types B and AB who received a test were more likely to test positive as were those who are Rh+ positive, and blood type O was less likely to test positive, which is in contrast with the above research.

Another paper was published on Nov. 13, 2020, in Nature Communication. The study used observational healthcare data on 14,112 individuals tested for COVID-19 with known blood type information in the New York Presbyterian (NYP) hospital system to assess the association between ABO and Rh blood types and infection, intubation, and death. The study found a slightly increased infection prevalence among non-O blood types. Risk of intubation was decreased among blood type A and increased among blood types AB and B, compared with blood type O. Risk of death was increased for blood type AB and decreased for blood types A and B.

Another paper published April 5, 2021, in JAMA Network Open, titled as “Association of sociodemographic factors and blood type with risk of COVID-19 in a U.S. population,” has reached a divergent conclusion. Through the Intermountain Healthcare (a non-profit, integrated health care system of 24 hospitals and 215 clinics in Utah, Idaho, and Nevada), the study searched and collected data for individuals who were tested for COVID-19 between March 3 and Nov. 2, 2020 and had a recorded blood type. A total of 107,796 individuals who had been tested for COVID-19 were included in the study. The study compared test results, hospitalization, whether presented to intensive care unit (ICU) or not. The study discovered no ABO blood types associations with either disease susceptibility or severity. The striking heterogeneity of reports from many prior studies could be due to chance variations, publication bias, differences in genetic background, geography and environment, and viral strains, according to this paper. The study considers that given the large and prospective nature of their study and its strongly null results, important associations of COVID-19 with ABO blood types are unlikely and will not be useful factors associated with disease susceptibility or severity on either an individual or population level for similar environments and ancestries.

Therefore, even though the three papers cited in the claim found a possible association between blood type and infectivity and severity of COVID-19, the relevant factors have not yet been confirmed, nor have the underlying biological mechanisms been proven. Different studies report contrasting results and have not yet reached an agreement on the association between blood type and infectivity and hospitalization rate of COVID-19. Based on the available information, this topic is still under debate in academia.