According to COVID-19 pandemic and its destructive effects on the economic and social situation, it is necessary to have a criterion for examining the epidemiology of this disease in different populations(11). With regard to a study on the incidence of COVID-19 in Iran, the population of male patients was higher than female ones. The highest incidence was reported in the age group of 21–50 years (12) According to the results obtained in this study, the number of male was considerably higher than female patients, and the mean age was 41.4 year which confirms the previous findings.
One of the issues that considered in the last decade is the study of susceptibility to viral infections such as HIV, hepatitis and influenza among people with different blood groups as an epidemiological indicator(2). This issue has also been considered in the corona pandemic as a link between blood groups and the development of COVID-19 infection. In a study by Bing Wu et al., people with blood type A were more susceptible to COVID-19 than other blood groups, while the least susceptibility belonged to people with blood type O(3). In another study conducted in 2021, the results showed a relative resistance of people with blood group O to SARS-COV-2 infection(13). In addition, in a study that evaluated the complications after COVID-19 infection, the results revealed that people with blood type B experienced more complications after infection than other blood groups, but there was no significant relationship between the incidence of the disease and blood types.(14)
One of the immune system responses against COVID-19 is hemorrhagic immunity and especially the production of IgG antibodies for more than 5 months on a stable basis. Therefore, community-based serological data are essential for understanding the true prevalence of infections- especially subclinical infections- because asymptomatic infections such as COVID- 19 are common, and such data allow making decisions about appropriate measures, epidemiological control, and accurate predictions of population mortality rates(4, 5)
A study aimed at serum prevalence of IgG antibodies among people aged 19 to 55 in Jazan province, Saudi Arabia in 2020 showed the high prevalence of serum IgG anti-SARS-COV-2 concentration with an approximate percentage of 26%, and the lowest value belonged to people under 18 years and over 56 years(15). Apart from that, evaluation of the serum prevalence of IgG antibody in people aged 20 to 75 years after the first wave of the COVID-19 epidemic in Geneva, Switzerland, confirmed the low prevalence of this antibody in individuals under 18 years and more than 60 years, while the highest level of IgG production was between 18 and 49 years old. The IgG level was low among children and people over 65 years of age.(16)
In our study, the mean IgG level of sample population was 7.06. and the level of this antibody in the age group between 25 to 50 years is significant, which could be consistent with the results of previous studies. In addition, the relationship between IgG levels and gender was examined, and its results indicated a significant relationship between the two. This amount of IgG was higher in men rather than in women. To complete the results of this study, IgG levels were measured in individuals with different ABO and Rh blood groups, but no significant relationship was found between these two parameters.
Our community-based serological study showed a high prevalence of SARS-CoV-2 antibodies in the population following the third wave of COVID-19 in Sanandaj, Iran. Serological levels of IgG antibodies were higher in adults than in children, indicating a higher risk of infection to COVID-19 in adults. Although no significant relationship was found between blood type and RH with the IgG level of COVID-19 patients, to understand the prevalence of the disease in the community and its epidemiological control, IgG antibody test is recommended to determine the serological level of the community, especially for those whose close relatives are infected with COVID-19 and have no specific symptoms. This screening can prevent the transmission of the disease to other people in the community and the beginning of a new wave of the disease.
Regarding the limitations in our study, we can refer to the limitations in the collected samples because these samples were collected only from Sanandaj City and did not include samples from all of Kurdistan Province. In addition, another limitation was related to the sampling of individuals after vaccination so that the results could finally be compared. Further clinical studies on relationship of blood types and immunologic responses in different communities are needed to reach a definitive conclusion in this regard.