Investigation and long-term monitoring of the presence of neutralizing antibody in patients with COVID-19 disease of different clinical severity.

Understanding the immune responses elicited by severe acute respiratory syndrome virus (SARS-CoV-2) infection is critical to public health policy and vaccine development and prevention of reinfections for COVID-19. It is important to know the neutralizing capacity of antibodies and to monitor their persistence. Patients with COVID-19 were divided into four groups (severe-critical, moderate, mild, and asymptomatic) according to their clinical severity. Antibodies against SARS-CoV-2 spike viral surface protein were investigated by ELISA method 3 and 9 months after the onset of the disease. Neutralizing antibody (NAb) response was evaluated by microneutralization test. Patients who received at least two doses of COVID-19 vaccine after illness were enrolled. SARS-CoV-2 immunoglobulin G (IgG) and NAb titers were shown to be strongly correlated with disease severity. Anti-SARS-CoV-2 IgG and NAb levels were found to be compatible with each other. After 9 months of follow-up, both IgG and NAb levels continued unabated in individuals who had the disease. In individuals who received at least two doses of the vaccine, these levels increased, except for severe-critical patients. High levels of anti-SARS-CoV-2 IgG are indicative, as it is difficult to investigate NAb in routine laboratories. At the same time, it can be predicted that this period may be much longer if it continues for at least 9 months and is reinforced with vaccination.

Humoral cross-reactivity towards SARS-CoV-2 in young children with acute respiratory infection with low-pathogenicity coronaviruses.

Background: SARS-CoV-2 infection in children frequently leads to only asymptomatic and mild infections. It has been suggested that frequent infections due to low-pathogenicity coronaviruses in children, impart immunity against SARS-CoV-2 in this age group. Methods: From a prospective birth cohort study prior to the pandemic, we identified children with proven low-pathogenicity coronavirus infections. Convalescent sera from these children were tested for antibodies against respective seasonal coronaviruses (OC43, NL63, and 229E) and SARS-CoV-2 by immunofluorescence and virus microneutralization assay respectively. Results: Forty-two children with proven seasonal coronavirus infection were included. Convalescent sera from these samples demonstrated antibodies against the respective seasonal coronaviruses. Of these, 40 serum samples showed no significant neutralization of SARS-CoV-2, while 2 samples showed inconclusive results. Conclusion: These findings suggest that the antibodies generated in low-pathogenicity coronavirus infections offer no protection from SARS-CoV-2 infection in young children.

An automated chemiluminescent immunoassay (CLIA) detects SARS-CoV-2 neutralizing antibody levels in COVID-19 patients and vaccinees.

OBJECTIVES: A specific and sensitive automated chemiluminescent immunoassay (CLIA) was developed to detect neutralizing antibody (NAb) levels. This assay can be used for the diagnosis of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection, treatment and vaccine evaluation. METHODS: The SARS-CoV-2 receptor-binding domain (RBD) and a stabilized version of the spike ectodomain as antigens were detected by CLIA. Sera NAb titers and concentrations from 860 SARS-CoV-2 vaccinees, 232 SARS-CoV-2 convalescent patients and 675 healthy individuals were tested by microneutralization test (MNT) and CLIA, respectively. Mathematical models were established to evaluate the relationship between two variables in different groups. CONCLUSIONS: With the RBD-based CLIA protocol, CLIA can be used to replace MNT to test SARS-CoV-2 NAb. Vaccine effectiveness, protectiveness and durability can be evaluated effectively by mathematical models. It is RESULTS: Analysing the relationship between NAb titers and concentrations, R2 for the decision-making tree was 0.870 and that of progressive linear fitting was 0.821. The receiver operating characteristic curve indicated specificity of 78.1%, sensitivity of 87.4%, cut-off value of 6.43 AU/mL and borderline range of 5.79-7.07 AU/mL for CLIA. Three-quarters (75.4%) of vaccinees were found to be NAb positive, and 5.35% vaccinees had NAb protective capability. The half-life of NAb in vaccinees was 10-11 weeks.for vaccinees to take a NAb assay periodically.

Development of indigenous IgG ELISA for the detection of anti-SARS-CoV-2 IgG.

BACKGROUND & OBJECTIVES: Since the beginning of the year 2020, the pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) impacted humankind adversely in almost all spheres of life. The virus belongs to the genus Betacoronavirus of the family Coronaviridae. SARS-CoV-2 causes the disease known as coronavirus disease 2019 (COVID-19) with mild-to-severe respiratory illness. The currently available diagnostic tools for the diagnosis of COVID-19 are mainly based on molecular assays. Real-time reverse transcription-polymerase chain reaction is the only diagnostic method currently recommended by the World Health Organization for COVID-19. With the rapid spread of SARS-CoV-2, it is necessary to utilize other tests, which would determine the burden of the disease as well as the spread of the outbreak. Considering the need for the development of such a screening test, an attempt was made to develop and evaluate an IgG-based ELISA for COVID-19. METHODS: A total of 513 blood samples (131 positive, 382 negative for SARS-CoV-2) were collected and tested by microneutralization test (MNT). Antigen stock of SARS-CoV-2 was prepared by propagating the virus in Vero CCL-81 cells. An IgG capture ELISA was developed for serological detection of anti-SARS-CoV-2 IgG in serum samples. The end point cut-off values were determined by using receiver operating characteristic (ROC) curve. Inter-assay variability was determined. RESULTS: The developed ELISA was found to be 92.37 per cent sensitive, 97.9 per cent specific, robust and reproducible. The positive and negative predictive values were 94.44 and 98.14 per cent, respectively. INTERPRETATION & CONCLUSIONS: This indigenously developed IgG ELISA was found to be sensitive and specific for the detection of anti-SARS-CoV-2 IgG in human serum samples. This assay may be used for determining seroprevalence of SARS-CoV-2 in a population exposed to the virus.