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Summary: Background: We measured the incidence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections and re-infections in an adult community-based cohort in southern India. Methods: We conducted a 2-year follow-up on 1229 participants enrolled between May and October 2021. Participants provided vaccination histories, weekly saliva samples, and blood samples at 0, 6, 12, and 24 months. Salivary reverse transcription polymerase chain reaction (RT-PCR) and Meso-Scale Discovery panels were used for SARS-CoV-2 detection and anti-spike, anti-nucleocapsid immunoglobulin G quantification. Whole genome sequencing was performed on a subset of positive samples. SARS-CoV-2 infection incidence was measured across Pre-Omicron (May–December 2021), Omicron-I (December 2021–June 2022), and Omicron-II (July 2022–October 2023) periods. Findings: In total, 1166 (95%) participants with 83% seropositivity at baseline completed the follow-up, providing 2205 person-years of observation. Utilizing both RT-PCR and serology we identified 1306 infections and yielded an incidence rate of 591.3 per 1000 person-years (95% confidence interval, 559.6–624.3), which peaked during Omicron-I at 1418.1 per 1000 person-years (95% confidence interval, 1307.4–1535.6). During Omicron-I and II, neither prior infection nor vaccination conferred protection against infection. Overall, 74% of infections were asymptomatic. Interpretation: Integrated RT-PCR and serology revealed significant SARS-CoV-2 infection frequency, highlighting the prevalence of asymptomatic cases among previously infected or vaccinated individuals. This underscores the effectiveness of combining surveillance strategies when monitoring pandemic trends and confirms the role of non-invasive sampling in ensuring participant compliance, reflecting national transmission patterns. Funding: The study was funded by the Bill and Melinda Gates Foundation.

Abstract Detailed characterisation of immune responses induced by COVID-19 vaccines rolled out in India: COVISHIELDTM (CS) and COVAXIN® (CO) in a pre-exposed population is only recently being discovered. We addressed this issue in subjects who received their primary series of vaccination between November 2021 and January 2022. Both vaccines are capable of strongly boosting Wuhan Spike-specific neutralising antibody, polyfunctional Th1 cytokine producing CD4+ T-cells and single IFN-γ + CD8+ T-cells. Consistent with inherent differences in vaccine platform, the vector-based CS vaccine-induced immunity was of greater magnitude, breadth, targeting Delta and Omicron variants compared to the whole-virion inactivated vaccine CO, with CS vaccinees showing persistent CD8+ T-cells responses until 3 months post primary vaccination. This study provides detailed evidence on the magnitude and quality of CS and CO vaccine induced responses in subjects with pre-existing SARS-CoV-2 immunity in India, thereby mitigating vaccine hesitancy arguments in such a population, which remains a global health challenge.

Background The durability of immune responses after vaccination against SARS CoV-2 in patients with autoimmune rheumatic diseases (AIRD) is not well studied. Objective We aimed to determine the longevity of humoral immune response to homologous vaccination with 2 doses of ChAdOx1 nCoV-19 and BBV152 in adult patients with AIRD. Methods In this prospective observational study, patients aged 18 to 60 years, diagnosed with SLE, primary systemic vasculitis and inflammatory arthritis (IA) who were scheduled to or had received vaccination with either ChAdOx1 nCoV-19 or BBV152 were recruited between June 2021 to March 2023. IgG antibodies against SARS CoV-2 spike protein (anti-S) were estimated in serum or plasma of patients prior to vaccination if feasible (T0), 15 to 28 days (T1), 75-100 days (T2), 170-190 days (T3), 240-290 days (T4), 340-370 days (T5) after receiving Vx2 by Diasorin chemiluminescence assay. The association of antibody titers with baseline parameters is estimated using chi-square or Mann Whitney tests using SPSS 16. Results Overall, 118 patients (93 females; age: 37.1, IQR: 28- 45 years; disease duration: 60 ((IQR) 29-103) months) with AIRD (SLE:48(40.6%), IA:53(44.9%), systemic vasculitis:7(5.9%) and spondyloarthropathy: 9(7.6%)) were recruited. Baseline demographic data has been depicted in (Table 1). The median antibody titer did not differ significantly between the two vaccines at T1 while the titers at T2, T3 and T4 were significantly lower for those vaccinated with BBV 152 (Table 2). The steroid dose prior to T1 and T2, intake of DMARDs in peri-vaccination period, type of AIRD (IA vs CTD) was not associated with significant difference in antibody titers at T1 and T2. Conclusion The anti-S humoral immune response persisted beyond 1 year for most of our patients with AIRD. After 3 months of vaccination, these responses were higher for ChAdOx1 nCoV-19 as compared with BBV152 in our patients with AIRD.

Introduction The incidence of SARS-CoV-2 re-infection has not been widely evaluated in low-income and middle-income countries. Understanding immune responses elicited by SARS-CoV-2 natural infection and factors that lead to re-infection in a community setting is important for public health policy. We aim to investigate the risk of primary infection and re-infection among those without and with evidence of prior infection as defined by the presence of antibodies to SARS-CoV-2 spike protein.Methods and analysis A baseline seroprevalence survey will test for SARS-CoV-2 antibodies among healthy adults in Vellore, India. Based on an expected seropositivity rate of 50% in the general population, with annual attack rates of 12%, 6%, 4.8% and 4% among those unvaccinated and seronegative, vaccinated and seronegative, unvaccinated and seropositive, and vaccinated and seropositive, respectively, we will recruit 1200 adults who will be followed up for a total of 24 months. Weekly self-collected saliva samples will be tested by reverse transcription-PCR (RT-PCR) to detect SARS-CoV-2 infections, for a period of 1 year. For any person testing RT-PCR positive, blood samples will be collected within 2 days of RT-PCR positivity and on days 30 and 90 to assess the kinetics and longevity of the antibody responses, B cell memory and T cell memory post-infection. The data will be analysed to estimate seroprevalence at baseline and over time, the risk factors for infection, rates of primary infection and re-infection, and provide a comparison of the rates across groups based on infection and vaccination status.Ethics and dissemination The study has been approved by the Institutional Review Board (IRB No: 13585) of Christian Medical College and Hospital, Vellore. The results of the study will be made available through journal publications and conference presentations.Trial registration number Central Trial Registry of India: CTRI/2020/11/029438.