Vaccination with BNT162b2 and ChAdOx1 nCoV-19 Induces Cross-Reactive Anti-RBD IgG against SARS-CoV-2 Variants including Omicron.

SARS-CoV-2 variants of concern (VOCs) have caused a significant increase in infections worldwide. Despite high vaccination rates in industrialized countries, the fourth VOC, Omicron, has outpaced the Delta variant and is causing breakthrough infections in individuals with two booster vaccinations. While the magnitude of morbidity and lethality is lower in Omicron, the infection rate and global spread are rapid. Using a specific IgG multipanel-ELISA with the spike protein's receptor-binding domain (RBD) from recombinant Alpha, Gamma, Delta, and Omicron variants, sera from health-care workers from the Medical University of Vienna were tested pre-pandemic and post-vaccination (BNT162b2; ChAdOx1 nCoV-19). The cohort was continuously monitored by SARS-CoV-2 testing and commercial nucleocapsid IgG ELISA. RBD IgG ELISA showed significantly lower reactivity against the Omicron-RBD compared to the Alpha variant in all individuals (p < 0.001). IgG levels were independent of sex, but were significantly higher in BNT162b2 recipients <45 years of age for Alpha, Gamma, and Delta (p < 0.001; p = 0.040; p = 0.004, respectively). Pre-pandemic cross-reactive anti-Omicron IgG was detected in 31 individuals and was increased 8.78-fold after vaccination, regardless of vaccine type. The low anti-RBD Omicron IgG level could explain the breakthrough infections and their presence could also contribute to a milder COVID-19 course by cross-reactivity and broadening the adaptive immunity.

Antibody Response against the SARS-CoV-2 Nucleocapsid Protein and Its Subdomains—Identification of Pre-Immunization Status by Human Coronaviruses with Multipanel Nucleocapsid Fragment Immunoblotting

A novel beta coronavirus that emerged in late December 2019 triggered a global pandemic. Diagnostic methods for rapid identification of infected individuals were established in new biotechnological approaches. Vaccine production and application to individuals and measurement of SARS-CoV-2 antibodies also began. Serum samples from 240 health care workers were collected at three-month intervals over nine months. Indirect SARS-CoV-2 nucleocapsid IgG ELISA tests were used to identify humoral immune responses. All seropositive individuals and those with borderline ELISA values were tested with a specifically generated multipanel nucleocapsid fragment immunoblot. Of the 240 individuals, 24 showed seroconversion in ELISA after experiencing COVID-19. All of them showed a positive reaction against the full-length nucleocapsid protein in the immunoblot. The highest reactivity was seen either against fragment N(100–300) or in a minority against the posterior part N(200–419). In general, the staining pattern of COVID-19 patients showed four phenotypes. In contrast, three individuals classified as borderline by ELISA reacted exclusively with fragments N(1–220) and N(100–300) containing the octamer amino acid sequence FYYLGTGP, which is identical in human coronaviruses sharing this sequence with SARS-CoV-2. These represent a unique and thus fifth phenotype. This work suggests the existence of distinct phenotypic patterns of IgG production towards N-protein subdomains.

COVID-19 serology in nephrology healthcare workers.

BACKGROUND: Chronic kidney disease patients show a high mortality in cases of a severe acute respiratory syndrome coronavirus-2 (SARS-CoV­2) infection. Thus, information on the sero-status of nephrology personnel might be crucial for patient protection; however, limited information exists about the presence of SARS-CoV­2 antibodies in asymptomatic individuals. METHODS: We examined the seroprevalence of SARS-CoV­2 IgG and IgM antibodies among healthcare workers of a tertiary care kidney center during the the first peak phase of the corona virus disease 2019 (COVID-19) crisis in Austria using an orthogonal test strategy and a total of 12 commercial nucleocapsid protein or spike glycoprotein-based assays as well as Western blotting and a neutralization assay. RESULTS: At baseline 60 of 235 study participants (25.5%, 95% confidence interval, CI 20.4-31.5%) were judged to be borderline positive or positive for IgM or IgG using a high sensitivity/low specificity threshold in one test system. Follow-up analysis after about 2 weeks revealed IgG positivity in 12 (5.1%, 95% CI: 2.9-8.8%) and IgM positivity in 6 (2.6%, 95% CI: 1.1-5.6) in at least one assay. Of the healthcare workers 2.1% (95% CI: 0.8-5.0%) showed IgG nucleocapsid antibodies in at least 2 assays. By contrast, positive controls with proven COVID-19 showed antibody positivity among almost all test systems. Moreover, serum samples obtained from healthcare workers did not show SARS-CoV­2 neutralizing capacity, in contrast to positive controls. CONCLUSION: Using a broad spectrum of antibody tests the present study revealed inconsistent results for SARS-CoV­2 seroprevalence among asymptomatic individuals, while this was not the case among COVID-19 patients. TRIAL REGISTRATION NUMBER: CONEC, ClinicalTrials.gov number NCT04347694.