Harmonization of Zika serological assays and comparative evaluation of two commercial ZIKA IgG ELISA kits.

The interpretation for Zika virus serology results is challenging due to high antibody cross reactivity with other flaviviruses. This limits availability of reliable and accurate methods for serosurveillance studies to understand the disease burden. Therefore, we conducted study to harmonize anti-Zika IgG antibody detection assays with 1st WHO International Standard (16/352) and working standard (16/320) for anti-Zika virus antibody.Additionally, evaluated NuGenTMZIKA-IgG and NovaLisa®ZIKA virus IgG-Capture ELISA using a panel of 278 seraFurther, 106 samples positive for other-flavi viruses were taken for assessing cross-reactivity of the assay, all serums were further tested by Zika-PRNT. The results of this study indicates satisfactory performance of both the assays. Serological and neutralization assays were calibrated according to the international standards. This will help in understanding antibody dynamics in serosurveillance and vaccine studies. However the performance of the kits with possibilities of cross-reactivity will have to be verified by coupling ZIKV and DENV specific ELISA.

External quality assurance of serological diagnosis of dengue, chikungunya and Japanese encephalitis virus infection.

Introduction: Dengue, chikungunya and Japanese encephalitis are the most common arthropod-borne viral diseases in India. Due to overlapping clinical symptoms, accurate, high-quality and timely laboratory-based differential diagnosis is essential for control and containment of outbreaks. This is most commonly done by detection of IgM antibodies in serum using enzyme-linked immunosorbent assays. The Resource Centre for Virus Research and Diagnostic Laboratories (VRDLs) in Pune, India organized an external quality assurance (EQA) study to check the accuracy of serological diagnostics in the VRDL network. Methods: Three panels, one each for anti-dengue virus, anti-chikungunya virus and anti-Japanese encephalitis virus IgM antibodies, comprising six human serum samples (two positive and four negative) were distributed to test the sensitivity, specificity and reproducibility of serological testing in 124 VRDLs across India in 2018-19 and 2019-20. Results: Among the 124 VRDLs, the average concordance for both 2018-19 and 2019-20 was 98%. In 2018-19, 78.33%, 13.33% and 6.66% of VRDLs reported 100% concordance, 91-99% concordance and 81-90% concordance with the reference results, respectively, and 1.66% of VRDLs had concordance <80%. In 2019-20, 79.68%, 14.06% and 4.68% of VRDLs reported 100% concordance, 91-99% concordance and 81-90% concordance with the reference results, respectively, and 1.56% of VRDLs had concordance <80%. Conclusion: The EQA programme was beneficial for assessing and understanding the performance of the VRDLs. The study data indicate good proficiency in serological diagnosis of dengue, chikungunya and Japanese encephalitis in the VRDL network laboratories. Further expansion of the EQA programme to cover other viruses of public health importance will increase confidence among the VRDL network, and generate evidence of high-quality testing.

Longitudinal clinico-serological analysis of anti-nucleocapsid and anti-receptor binding domain of spike protein antibodies against SARS-CoV-2.

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.

Performance assessment of seven SARS-CoV-2 IgG enzyme-linked immunosorbent assays.

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.