Sero-Surveillance to Monitor the Trend of SARS-CoV-2 Infection Transmission in India: Study Protocol for a Multi Site, Community Based Longitudinal Cohort Study.

Introduction: Large-scale sero-prevalence studies with representation from all age groups are required to estimate the true burden of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in the community. Serial serological surveys in fixed cohorts enable study of dynamics of viral transmission and correlates of immune response over time in the context of gradual introduction of COVID-19 vaccines and repeated upsurge of cases during the pandemic. Methods: This longitudinal study will involve follow-up of a cohort of 25,000 individuals (5,000 per site) aged 2 years and above recruited from five existing demographic surveillance sites in India. The cohort will be tested for the presence of IgG antibodies against S1/S2 spike protein subunits of SARS-CoV-2 in four rounds; once at baseline and subsequently, at intervals of 4 months for a year between January 2021 and January 2022. Neutralization assays will be carried out in a subset of seropositive samples in each round to quantify the antibody response and to estimate the durability of antibody response. Serial serological surveys will be complemented by fortnightly phone based syndromic surveillance to assess the burden of symptomatic acute febrile illness/ influenza like illness in the same cohort. A bio-repository will also be established to store the serum samples collected in all rounds of serological surveys. Discussion: The population based sero-epidemiological studies will help to determine the burden of COVID-19 at the community level in urban and rural Indian populations and guide in monitoring the trends in the transmission of SARS-CoV-2 infection. Risk factors for infection will be identified to inform future control strategies. The serial serological surveys in the same set of participants will help determine the viral transmission dynamics and durability of neutralizing immune response in participants with or without symptomatic COVID infection.

Cohort profile: Indian Network of Population-Based Surveillance Platforms for Influenza and Other Respiratory Viruses among the Elderly (INSPIRE).

PURPOSE: We describe here a multicentric community-dwelling cohort of older adults (>60 years of age) established to estimate incidence, study risk factors, healthcare utilisation and economic burden associated with influenza and respiratory syncytial virus (RSV) in India. PARTICIPANTS: The four sites of this cohort are in northern (Ballabgarh), southern (Chennai), eastern (Kolkata) and western (Pune) parts of India. We enrolled 5336 participants across 4220 households and began surveillance in July 2018 for viral respiratory infections with additional participants enrolled annually. Trained field workers collected data about individual-level and household-level risk factors at enrolment and quarterly assessed frailty and grip strength. Trained nurses surveilled weekly to identify acute respiratory infections (ARI) and clinically assessed individuals to diagnose acute lower respiratory infection (ALRI) as per protocol. Nasal and oropharyngeal swabs are collected from all ALRI cases and one-fifth of the other ARI cases for laboratory testing. Cost data of the episode are collected using the WHO approach for estimating the economic burden of seasonal influenza. Handheld tablets with Open Data Kit platform were used for data collection. FINDINGS TO DATE: The attrition of 352 participants due to migration and deaths was offset by enrolling 680 new entrants in the second year. All four sites reported negligible influenza vaccination uptake (0.1%-0.4%), low health insurance coverage (0.4%-22%) and high tobacco use (19%-52%). Ballabgarh had the highest proportion (54.4%) of households in the richest wealth quintile, but reported high solid fuel use (92%). Frailty levels were highest in Kolkata (11.3%) and lowest in Pune (6.8%). The Chennai cohort had highest self-reported morbidity (90.1%). FUTURE PLANS: The findings of this cohort will be used to inform prioritisation of strategies for influenza and RSV control for older adults in India. We also plan to conduct epidemiological studies of SARS-CoV-2 using this platform.