Assessment of Diagnostic Specificity of Anti-SARS-CoV-2 Antibody Tests and Their Application for Monitoring of Seroconversion and Stability of Antiviral Antibody Response in Healthcare Workers in Moscow

Abstract

Anti-SARS-CoV-2 antibody testing is an efficient tool to assess the proportion of seropositive population due to infection and/or vaccination. Numerous test systems utilizing various antigen composition(s) are routinely used for detection and quantitation of anti-SARS-CoV-2 antibodies. We determined their diagnostic specificity using archived true-negative samples collected before the onset of the COVID-19 pandemic. Using test systems demonstrating 98.5–100% specificity, we assessed the dynamics of SARS-CoV-2 seroconversion and durability of anti-spike (S) antibodies in healthcare professionals (n = 100) working in Moscow during the first two cycles of the pandemic (May 2020 to June 2021) outside of the “red zone”. Analysis revealed a rapid increase in anti-SARS-CoV-2 seropositivity from 19 to 80% (19/100 and 80/100, respectively) due to virus exposition/infection; only 16.3% of seroconversion cases (13/80) were due to vaccination, but not the virus exposure, although massive COVID-19 vaccination of healthcare workers was performed beginning in December 2020. In total, 12.7% (8/63) remained positive for anti-SARS-CoV-2 IgM for >6 months, indicating unsuitability of IgM for identification of newly infected individuals. All except one remained seropositive for anti-S antibodies for >9 months on average. Significant (>15%) declines in anti-SARS-CoV-2 antibody concentrations were observed in only 18% of individuals (9/50). Our data on the high seropositivity rate and stability of anti-SARS-CoV-2 antibody levels in healthcare personnel working outside of the “red zone” indicate their regular exposition to SARS-CoV-2/an increased risk of infection, while a low frequency of vaccine-induced antibody response acquired after the start of vaccination points to vaccine hesitancy.

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“…Kichatova et al surveyed the frequency and duration of the infection-induced antibody response to SARS-CoV-2 and assessed the diagnostic specificity of antibody tests and their application for monitoring of antibody responses to infection and to COVID-19 vaccines [6]. Among the findings of this study was the observation of a high degree of seropositivity to SARS-CoV-2 in non-vaccinated health care workers due to workplace exposure to the virus [6].…”

“…The focus of the studies by Tran et al [4], Tuchynskaya et al [5] and Kichatova et al [6] was anti-viral antibody responses. Tran et al developed a virus-like particle (VLP)-based vaccine on the backbone of the attenuated Kunjin strain of the West Nile virus and utilized it as a delivery system for the Ebola virus glycoprotein and the matrix protein genes.…”

“…The level of virus-neutralizing antibodies after the challenge was influenced by the ratio of non-infectious to infectious viral particles in the challenge virus; however, the latter had no effect on the protectivity [5]. Kichatova et al surveyed the frequency and duration of the infection-induced antibody response to SARS-CoV-2 and assessed the diagnostic specificity of antibody tests and their application for monitoring of antibody responses to infection and to COVID-19 vaccines [6]. Among the findings of this study was the observation of a high degree of seropositivity to SARS-CoV-2 in non-vaccinated health care workers due to workplace exposure to the virus [6].…”