Assessment of humoral immunity to SARS-CoV-2 by a sample examination of medical workers in a large specialized multidisciplinary hospital

Abstract

Introduction. The assessment of specific IgG antibodies to RBD Spike SARS-CoV-2 and their quantitation permit to calculate the intensity of immunity to COVID-19, i.e. to determine the level of immunity to infection, the risk of infection, the severity of the disease, as well as the ability to prevent death. Meanwhile, the protective level of antibodies is not determined. Therefore, determining the nature of immunity and quantitation of IgG antibodies to RBD Spike SARS-CoV-2 make it possible to assess the effectiveness of preventive measures and correct them in a timely manner.
 The aim is to determine the presence of IgG antibodies to RBD Spike SARS-CoV-2, their concentrations, and the nature of humoral immunity in different age and occupational groups of employees in a closed-type hospital after the completed vaccination with "Gam-Covid-Vac" vaccine.
 Materials and methods. The blood sera of 310 members of medical staff who received a full course of immunization with the "Gam-Covid-Vac" vaccine were tested using "SARS-CoV-2-ELISA-IgG" kit according to instructions provided in 21.20.23-004-28597318-2020, RU No. RZN 2021/15898. IgG antibodies to RBD Spike SARS-CoV-2 were quantitated against WHO standard NIBSC 20/136.
 Results. Specific IgG antibodies to RBD Spike SARS-CoV-2 were found in 92.9% of the examined individuals, including 67.4% having hybrid immunity (both vaccine- and infection- induced), and 25.5% having post-vaccination immunity after immunization with the "Gam-Covid-Vac" vaccine; 7.1% participants were nonimmune. A higher level of IgG antibodies to RBD Spike SARS-CoV-2 was detected in the group of individuals with hybrid immunity (p 0.01). Only 11.6% of employees had a protective antibody level of more than 300 BAU/ml.
 Discussion. Most employees with hybrid immunity were identified in the older age groups and in the junior medical staff. The results of this serological study, taking into account the age and professional aspects, can serve as the basis for adjusting preventive measures in medical institutions.