Prevalence of SARS-CoV-2 antibodies before COVID-19 pandemic among vulnerable population groups in Ukraine
Authors: Maksymenok O. V. ,   SI «The L. V. Hromashevskyi Institute of Epidemiology and Infectious Diseases of National Academy of Medical Sciences of Ukraine», Kyslykh O.M. , Serheieva T. A. 
Published: July 2024

S erological studies aimed at determining antibodies to SARS-CoV-2 (AВ-SARS-CoV-2) in the first stages of the pandemic became an effective tool for assessing the intensity of the epidemic process of COVID-19. Diagnostic kits were primarily intended to be used in studies (mainly sero-epidemiological) at the population level, and not for individual diagnosis of COVID-19 cases. However, for a correct assessment of the prevalence of AВ-SARS-CoV-2 during the epidemic period, it is advisable to operate with the initial data regarding the detection of the specified markers in the pre-epidemic period. For a long time, it was discussed whether SARS-CoV-2 is really a new virus, or whether it was circulating in the human population even before the pandemic. Thus, according to some authors, one of the questions that needs to be solved is the determination of when SARS-CoV-2 began to spread among humans, since a growing number of different studies provide evidence that the virus could spread around the world for weeks or even months until now. In contrast, other researchers believe that the positive results of detection of AT-SARS- CoV-2 before the beginning of the epidemic are more likely to be related to false positive test results. Therefore, it was of interest to investigate whether blood serum samples collected before the beginning of the COVID-19 epidemic contain serological markers of SARS-CoV-2, which could indicate, on the one hand, the hidden circulation of the infectious agent long before the beginning of the epidemic, and on the other , which seems more likely - about the cross-reactivity of antibodies to different coronaviruses, which are more often observed in people with various pathological conditions, accompanied by a compromise of the immune system. The purpose of the study. To estimate the prevalence of AB-SARS-CoV-2 among certain population groups of Ukraine with a compromised immune response before the start of the COVID-19 epidemic and after its official end. Materials and methods. The seroprevalence of SARS-CoV-2 was retrospectively studied in 837 blood serum samples, including: 465 samples obtained during 2010 from people who use injection drugs (IDUs) during sentinel studies by the unlinked method anonymous testing; 372 — anonymous samples obtained in 2009 from patients on systemic hemodialysis. A separate panel of sera consisted of 93 anonymous samples from HIV-positive individuals obtained during 2024. The materials were stored in a freezer at a temperature of -20 °C and were thawed immediately before testing. Determination of serological markers of COVID-19 was carried out by the ELISA method using test systems for the detection of antibodies of the IgG class to the SARS-CoV-2 nucleocapsid protein «DIA®-SARS-CoV-2NP-IgG» («DIAPROF-MED», Ukraine).Results. In our study, we used blood serum samples of 465 IDUs collected during 2010. Among the materials studied, 350 (75.3±2.0)% of the samples were obtained from men, 115 (24.7±2.0)% from women The average age of the examinees was (30.4±2.1) years, the largest number of representatives of IDUs belonged to the age groups of 20–24 and 25–34 years. When carrying out studies using the ELISA method for the presence of IgG class antibodies to the nucleocapsid protein of SARS-CoV-2, 17 (3.7±0.9%, 95% CI: 5.4–2.0) positive findings were found, among them 13 ( 3.7%, 95% CI: 3.5–3.9) samples were obtained from men, 4 (3.5%, 95% CI: 3.2–3.8) — from women. There was no significant difference in the detection frequency of AT-SARS-CoV-2 in men and women (t=0.09, p=0.93). During the examination of blood serum samples of 372 patients on hemodialysis, 18 (4.8±1.1%, CI: 2.6–6.9) were found to have antibodies to the SARS-CoV-2 nucleocapsid antigen, with significant differences between the recorded percentages positive results and the percentage of positive results in the IDUs group were not registered (t=0.77, p=0.43). Among the specified 18 blood serum samples positive for AB-SARS-CoV-2, 8 (44.4±11.7%) contained antibodies to HCV and the core antigen (HBc) of the hepatitis B virus (HBV), two samples — (11.1±7.4%) — HBV HBsAg. Among 354 samples negative for AB-SARS-CoV-2, the specified markers were determined in a smaller proportion: antibodies to HCV were recorded in 100 samples (28.2±2.4%), antibodies to HBc, HBsAg HBV — in 150 (42.4±2.6%) and 19 (5.4±1.2%) samples, respectively, but the difference between the frequency of detection of markers in both groups was not reliable. In our opinion, the relatively small percentage of positive results of detection of AB-SARS-CoV-2 in IDUs and patients on hemodialysis rather indicates cross-reactivity with other coronaviruses, which, in turn, can be considered as a proxy indicator of the spread of coronaviruses in the population. The prevalence of AB-SARS-CoV-2 in HIV-positive persons was expected to be significant — out of 93 tested samples, 56 (60.2±5.1%) were positive, however, compared to the data of the 2023 study, this indicator turned out to be significantly lower (t=4.8, p<0.001). It is possible that the obtained difference in the detection rates of AB-SARS-CoV-2 is associated with differences in the period of the epidemic, namely with a decrease in the intensity of the epidemic process of COVID-19, and the elimination of antibodies that were formed as a result of earlier vaccination is not excluded. Conclusions. When serum samples of people with a compromised immune system, deposited in 2009–2010, were tested for the presence of antibodies to SARS-CoV-2, the number of positive results was 3.7% in people who use injection drugs, and 4.8% in patients receiving hemodialysis. Such proportions of the antibodies frequency detection correspond to the seroprevalence of COVID-19 at the initial stage of the epidemic. No difference was found in the frequency of detection of antibodies to SARS-CoV-2 in the study of blood serum samples of patients on hemodialysis, depending on HBV-/HCV-infection as possible factors of false-positive results of detection of AB-SARS-CoV-2. Among HIV-positive persons examined in 2024, the seroprevalence of COVID-19 was 60.2%, which is significantly lower than when examining persons from this vulnerable group in 2023 (85.9%). The determined level of seroprevalence of AB-SARS-CoV-2 in serum samples of people who use injection drugs and patients on hemodialysis can be considered as a background indicator of the prevalence of coronaviruses among representatives of vulnerable population groups. Key words: seroprevalence, antibodies to SARS-CoV-2, vulnerable population groups.