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Objectives Monitoring the antibody responses to SARS-CoV-2 infection and its correlation to clinical spectrum of disease is critical in understanding the disease progression and protection against re-infection. We assessed the nucleocapsid (N) and receptor-binding-domain of spike (SRBD) protein specific IgG and neutralizing antibody (NAb) responses in COVID-19 patients up to 8 months and its correlation with diverse disease spectrum. Methods During the first wave of the SARS-CoV-2 pandemic, from 284 COVID-19 patients, 608 samples were collected up to 8 months post infection. The patients were categorized as asymptomatic, symptomatic and severe. The N and SRBD IgG and NAb titers were evaluated and correlated with clinical data. Results A steep increase in antigen specific antibody titers was observed till 40 days post onset of the disease (POD), followed by a partial decline till 240 days. Severe disease was associated with a stronger SRBD IgG response and higher NAb titers. The persistence of antibody response was observed in 76% against N, 80% against SRBD and 80% for NAbs of cases up to 8 months POD. Conclusion RBD and N protein specific IgG persisted till 240 days POD which correlated with NAb response, irrespective of individual`s symptomatic status indicating overall robust protection against re-infection.

The pandemic of COVID‐19 has caused enormous fatalities worldwide. Serological assays are important for detection of asymptomatic or mild cases of COVID‐19, and sero‐prevalence and vaccine efficacy studies. Here, we evaluated and compared the performance of seven commercially available enzyme‐linked immunosorbent assay (ELISA)s for detection of anti‐severe acute respiratory syndrome corona virus 2 (SARS‐CoV‐2) immunoglobulin G (IgG). The ELISAs were evaluated with a characterized panel of 100 serum samples from qRT‐PCR confirmed COVID‐19 patients, collected 14 days post onset disease, 100 SARS‐CoV‐2 negative samples and compared the results with that of neutralization assay. Results were analysed by creating the receiver operating characteristic curve of all the assays in reference to the neutralization assay. All kits, were found to be suitable for detection of IgG against SARS‐CoV‐2 with high accuracy. The DiaPro COVID‐19 IgG ELISA showed the highest sensitivity (98%) among the kits. The assays demonstrated high sensitivity and specificity in detecting the IgG antibodies against SARS‐CoV‐2. However, the presence of IgG antibodies does not always correspond to neutralizing antibodies. Due to their good accuracy indices, these assays can also aid in tracing mild infections, in cohort studies and in pre‐vaccine evaluations.

Background & objectives: The global pandemic caused by SARS-CoV-2 virus has challenged public health system worldwide due to the unavailability of approved preventive and therapeutic options. Identification of neutralizing antibodies (NAb) and understanding their role is important. However, the data on kinetics of NAb response among COVID-19 patients are unclear. To understand the NAb response in COVID-19 patients, we compared the findings of microneutralization test (MNT) and plaque reduction neutralization test (PRNT) for the SARS-CoV-2. Further, the kinetics of NAb response among COVID-19 patients was assessed. Methods: A total of 343 blood samples (89 positive, 58 negative for SARS-CoV-2 and 17 cross-reactive and 179 serum from healthy individuals) were collected and tested by MNT and PRNT. SARS-CoV-2 virus was prepared by propagating the virus in Vero CCL-81 cells. The intra-class correlation was calculated to assess the correlation between MNT and PRNT. The neutralizing endpoint as the reduction in the number of plaque count by 90 per cent (PRNT90) was also calculated. Results: The analysis of MNT and PRNT quantitative results indicated that the intra-class correlation was 0.520. Of the 89 confirmed COVID-19 patients, 64 (71.9%) showed NAb response. Interpretation & conclusions: The results of MNT and PRNT were specific with no cross-reactivity. In the early stages of infection, the NAb response was observed with variable antibody kinetics. The neutralization assays can be used for titration of NAb in recovered/vaccinated or infected COVID-19 patients.

The pandemic of COVID -19 caused by SARS-CoV-2 is leading to a humongous impact on the mankind with over a million people succumbing to it worldwide. Although there are few drugs approved for the treatment, there is not yet a safe and effective vaccine available for COVID-19. Also, the passive immunization therapy with convalescent plasma, though potentially an effective treatment option for other viral disease has limitation of availability. The prior use of immunoglobulins generated in animals has proven to be effective in several viral and bacterial diseases. Here, we report the development and evaluation of equine hyper immune globulin raised against inactivated SARS-CoV-2 virus. Post immunization neutralization titres of the equines demonstrated high neutralizing antibodies. To minimize the adverse effects, the immunoglobulins were digested with pepsin, and purified to obtain the F(ab’)2 fragments. The average nAb titre of the purified bulk was 22,927 and correlated with high IgG binding efficiency in ELISA. The quality control assessments of the different batches proved to have consistent nAb titres. The study provides evidence of the potential of generating highly purified F(ab’)2 from equines against SARS-CoV-2 that can demonstrate consistent and high neutralization activity. Further, in-vivo testing for efficacy of this indigenously developed, cost effective product will pave the way to clinical evaluation.