Seroprevalence of IgG antibodies against SARS-CoV-2 among the general population and healthcare workers in India, June-July 2021: A population-based cross-sectional study

• Published in: PLoS medicine 2021-12, Vol.18 (12), p.e1003877
• Main Authors: Murhekar, Manoj V, Bhatnagar, Tarun, Thangaraj, Jeromie Wesley Vivian, Saravanakumar, V, Santhosh Kumar, Muthusamy, Selvaraju, Sriram, Rade, Kiran, Kumar, C P Girish, Sabarinathan, R, Asthana, Smita, Balachandar, Rakesh, Bangar, Sampada Dipak, Bansal, Avi Kumar, Bhat, Jyothi, Chakraborty, Debjit, Chopra, Vishal, Das, Dasarathi, Devi, Kangjam Rekha, Dwivedi, Gaurav Raj, Jain, Agam, Khan, S Muhammad Salim, Kumar, M Sunil, Laxmaiah, Avula, Madhukar, Major, Mahapatra, Amarendra, Ramesh, Talluri, Rangaraju, Chethana, Turuk, Jyotirmayee, Yadav, Suresh, Bhargava, Balram
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Aged; Antibodies; Biology and Life Sciences; Chemiluminescence; Child; Consent; Coronaviruses; COVID-19; COVID-19 - blood; COVID-19 - epidemiology; COVID-19 - immunology; COVID-19 diagnostic tests; COVID-19 vaccines; Cross-Sectional Studies; Epidemiology; Female; Health aspects; Health care; Health Personnel; Households; Humans; Immunization; Immunoglobulin G; Immunoglobulin G - blood; India - epidemiology; Infections; Laboratories; Male; Medical personnel; Medicine and Health Sciences; Middle Aged; Nucleocapsids; People and Places; Population; Population studies; Population-based studies; Prevalence; Proteins; Public health; Rural Population; SARS-CoV-2; Serology; Severe acute respiratory syndrome coronavirus 2; Statistics; Teams; Urban Population; Vaccination; Vaccines; Young Adult
• ISSN: 1549-1676; 1549-1277; 1549-1676
• DOI: 10.1371/journal.pmed.1003877

India began COVID-19 vaccination in January 2021, initially targeting healthcare and frontline workers. The vaccination strategy was expanded in a phased manner and currently covers all individuals aged 18 years and above. India experienced a severe second wave of COVID-19 during March-June 2021. We conducted a fourth nationwide serosurvey to estimate prevalence of SARS-CoV-2 antibodies in the general population aged ≥6 years and healthcare workers (HCWs). We did a cross-sectional study between 14 June and 6 July 2021 in the same 70 districts across 20 states and 1 union territory where 3 previous rounds of serosurveys were conducted. From each district, 10 clusters (villages in rural areas and wards in urban areas) were selected by the probability proportional to population size method. From each district, a minimum of 400 individuals aged ≥6 years from the general population (40 individuals from each cluster) and 100 HCWs from the district public health facilities were included. The serum samples were tested for the presence of IgG antibodies against S1-RBD and nucleocapsid protein of SARS-CoV-2 using chemiluminescence immunoassay. We estimated the weighted and test-adjusted seroprevalence of IgG antibodies against SARS-CoV-2, along with 95% CIs, based on the presence of antibodies to S1-RBD and/or nucleocapsid protein. Of the 28,975 individuals who participated in the survey, 2,892 (10%) were aged 6-9 years, 5,798 (20%) were aged 10-17 years, and 20,285 (70%) were aged ≥18 years; 15,160 (52.3%) participants were female, and 21,794 (75.2%) resided in rural areas. The weighted and test-adjusted prevalence of IgG antibodies against S1-RBD and/or nucleocapsid protein among the general population aged ≥6 years was 67.6% (95% CI 66.4% to 68.7%). Seroprevalence increased with age (p < 0.001) and was not different in rural and urban areas (p = 0.822). Compared to unvaccinated adults (62.3%, 95% CI 60.9% to 63.7%), seroprevalence was significantly higher among individuals who had received 1 vaccine dose (81.0%, 95% CI 79.6% to 82.3%, p < 0.001) and 2 vaccine doses (89.8%, 95% CI 88.4% to 91.1%, p < 0.001). The seroprevalence of IgG antibodies among 7,252 HCWs was 85.2% (95% CI 83.5% to 86.7%). Important limitations of the study include the survey design, which was aimed to estimate seroprevalence at the national level and not at a sub-national level, and the non-participation of 19% of eligible individuals in the survey. Nearly two-thirds of individuals aged ≥6