The COVID-19 pandemic has resulted in several waves of infection in many countries worldwide. The significant variations in case fatality ratio among different geographical regions suggest that the human susceptibility against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) varies substantially.
Scientists worldwide are conducting extensive research to understand the nature of the virus, its transmission kinetics, etc. They have found a strong correlation between the ABO blood group and SARS-CoV-2 regarding its morbidity and mortality.
Previous studies have shown the relationship between the ABO blood group and several viral diseases. Researchers have reported that among the people inhabiting the Indian Gangetic plain, individuals with the blood group O are most vulnerable to cholera and Helicobacter pylori infection. Nevertheless, this blood group was reported to be less susceptible to dengue and SARS (Severe Acute Respiratory Syndrome) viruses.
The ABO blood type is determined by the gene ABO, present at chromosome 9. Several pieces of research have indicated that this gene directly or indirectly moderates an individual's COVID-19 susceptibility. Further research reported that some of the variants of this gene might play an important role that affects the morbidity and mortality of many diseases, including COVID-19. For instance, the ABO gene influences red blood cell-related physiology, type 2 diabetes, venous thromboembolism, heart-related functions, ischemic stroke, and coronary artery disease. Scientists believe that understanding how ABO blood type affects SARS-CoV-2 infection is essential, as it could help determine the factors which make an individual susceptible to SARS-CoV-2.
Now, new research that focuses on the association between an individual having blood group ABO and being asymptomatic COVID-19 positive is published on the medRxiv* preprint server. This is the first report which deals with the association between blood group and the incidence of asymptomatic COVID-19 infection.
This study used random serosurveillance and blood group testing of street vendors in northern India. The data was collected from 509 individuals from three districts of the eastern Uttar Pradesh region. Researchers have reported that the seroprevalence of all the districts considered in this study was greater than 0.4. This increased seroprevalence indicates that the majority of SARS-CoV-2 infections were owing to asymptomatic infections. Even though seroprevalence is not uniform in all India's districts, many independent regions reported a high level of seroprevalence. Thereby, seroprevalence is found to be sporadic rather than uniform.
In the current research, among 509 samples, the frequency distribution for blood groups A, B, O, and AB was found to be 0.204, 0.354, 0.279, and 0.163, respectively. Scientists reported that blood group B is the most common type in the eastern Uttar Pradesh region, followed by blood group O and the least common blood group was AB. To verify if this data represents the true distribution of the blood group of the region, scientists obtained published data of the same region and carried out a regression analysis. Thereby, the adjusted R square value (96.7% +2.7%) revealed a high level of correlation between the data (current study) and the previously published data. This result indicated that the data considered for the current study truly represented the regional distribution of the blood groups.
The blood group of SARS-CoV-2 infected individuals was estimated and grouped. Scientists have reported that the ABO blood group distribution of 215 seropositive people showed 0.223, 0.312, 0.107, and 0.358 frequency of A, B, O, and AB blood groups, respectively. In this study, a considerable inconsistency was found in the relative blood group distribution, especially between O and AB. Among the seropositive group, the blood group AB was significantly higher, while blood group O was significantly lower. This result is similar to the previously published data on seropositive individuals. Thereby, the current research has established a strong association of blood groups O and AB with COVID-19 susceptibility.
While assessing which blood group is more at risk of COVID-19 infection, scientists revealed that individuals with blood group AB are at a much higher risk of getting COVID-19 infection than individuals with blood group O type. This research developed a risk scale which indicated that individuals with blood group AB are most susceptible or at the highest risk of being infected with SARS-CoV-2, followed by blood group A and B. However, blood group O is placed at the lower end of this risk scale, indicating this blood group is at a considerably lower risk of being infected. Previous research stated that Rh-negative blood type plays a protective role against SARS-CoV-2. This study did not find any link between the Rh factor and COVID-19. However, it must be mentioned that there were a limited number of Rh-negative samples.
One of the limitations of this study is that it did not consider data on individuals who are severely infected with SARS-CoV-2. Thereby, the relationship between blood group and COVID-19 severity is not projected. However, one interesting outcome of the research is that even though the AB blood group is most susceptible to COVID-19 infection, it may not be at a high risk of severity. A larger data would help to draw more decisive conclusions.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.