Differential Sars-Cov-2 Antigen Specificity of the Humoral Response in Inactivated Virus-Vaccinated, Convalescent, and Breakthrough Subjects

Abstract

Analytical methods for the differential determination between natural infection with SARS-CoV-2 vs. immunity elicited by vaccination or infection after immunization (breakthrough cases) represent attractive new research venues in the context of the ongoing COVID-19 pandemic caused by Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2). Herein, we set out to compare humoral responses against several SARS-CoV-2 structural and non-structural proteins in infected unvaccinated (convalescent), vaccinated, as well as vaccinated and infected (breakthrough) individuals. Our results indicate that immunization with an inactivated SARS-CoV-2 vaccine (CoronaVac) induces significantly higher levels of IgG antibodies against the membrane (M) protein of SARS-CoV-2 as compared to convalescent subjects both, after the primary vaccination schedule and after a booster dose. Moreover, we found that CoronaVac-immunized individuals, after receiving a third vaccine shot, display equivalent levels of N-specific IgG antibodies as convalescents subjects. Regarding non-structural viral proteins, for the two viral proteins ORF3a and NSP8, IgG antibodies were produced in more than 50% of the convalescent subjects. Finally, a logistic regression model and a receiver operating characteristic (ROC) analysis show that combined detection of M and N proteins may be useful as a biomarker to differentiate breakthrough cases from vaccinated and convalescent individuals that did not receive prior vaccination. Taken together, these results suggest that multiple SARS-CoV-2 antigens may be used as differential biomarkers for distinguishing natural infection from vaccination.

Antibody response to symptomatic infection with SARS-CoV-2 Omicron variant viruses, December 2021—June 2022

“…However, data, though limited, suggests that vaccination status and pre-existing neutralizing antibodies may affect anti-N antibody response by altering viral load in early illness [8, 16]. Measurement of immune response to infection and antibody levels after convalescence could improve understanding of vaccinated cases and hybrid immunity [17].…”

Antibody Response to Symptomatic Infection With SARS‐CoV‐2 Omicron Variant Viruses, December 2021–June 2022

“…The serologic assay used in our study contained ancestral SARS‐CoV‐2 antigens, and concentrations were converted to binding antibody units using WHO international serum standards from early in the COVID‐19 response. Against pre‐Omicron variants, virus neutralization titers and IgG antibody concentrations were associated with protection; however, antibody binding concentrations and neutralization activity were lower against Omicron variants [2, 8, 18]. In addition, anti‐N bAb seropositivity cut‐off values were based on mean fluorescence intensity using serum standards rather than DBS [9, 13].…”