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Summary Background Diphtheria is re-emerging as a public health problem in several Indian states. Most diphtheria cases are among children older than 5 years. In this study, we aimed to estimate age-specific immunity against diphtheria in children aged 5–17 years in India. Methods We used residual serum samples from a cross-sectional, population-based serosurvey for dengue infection done between June 19, 2017, and April 12, 2018, to estimate the age-group-specific seroprevalence of antibodies to diphtheria in children aged 5–17 years in India. 8309 serum samples collected from 240 clusters (122 urban and 118 rural) in 60 selected districts of 15 Indian states spread across all five geographical regions (north, northeast, east, west, and south) of India were tested for the presence of IgG antibodies against diphtheria toxoid using an ELISA. We considered children with antibody concentrations of 0·1 IU/mL or greater as immune, those with levels less than 0·01 IU/mL as non-immune (and hence susceptible to diphtheria), and those with levels in the range of 0·01 to less than 0·1 IU/mL as partially immune. We calculated the weighted proportion of children who were immune, partially immune, and non-immune, with 95% CIs, for each geographical region by age group, sex, and area of residence (urban vs rural). Findings 29·7% (95% CI 26·3–33·4) of 8309 children aged 5–17 years were immune to diphtheria, 10·5% (8·6–12·8) were non-immune, and 59·8% (56·3–63·1) were partially immune. The proportion of children aged 5–17 years who were non-immune to diphtheria ranged from 6·0% (4·2–8·3) in the south to 16·8% (11·2–24·4) in the northeast. Overall, 9·9% (7·7–12·5) of children residing in rural areas and 13·1% (10·2–16·6) residing in urban areas were non-immune to diphtheria. A higher proportion of girls than boys were non-immune to diphtheria in the northern (17·7% [12·6–24·2] vs 7·1% [4·1–11·9]; p=0·0007) and northeastern regions (20·0% [12·9–29·8] vs 12·9% [8·6–19·0]; p=0·0035). Interpretation The findings of our serosurvey indicate that a substantial proportion of children aged 5–17 years were non-immune or partially immune to diphtheria. Transmission of diphtheria is likely to continue in India until the immunity gap is bridged through adequate coverage of primary and booster doses of diphtheria vaccine. Funding Indian Council of Medical Research.

BACKGROUND: The first national severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serosurvey in India, done in May-June, 2020, among adults aged 18 years or older from 21 states, found a SARS-CoV-2 IgG antibody seroprevalence of 0·73% (95% CI 0·34-1·13). We aimed to assess the more recent nationwide seroprevalence in the general population in India. METHODS: We did a second household serosurvey among individuals aged 10 years or older in the same 700 villages or wards within 70 districts in India that were included in the first serosurvey. Individuals aged younger than 10 years and households that did not respond at the time of survey were excluded. Participants were interviewed to collect information on sociodemographics, symptoms suggestive of COVID-19, exposure history to laboratory-confirmed COVID-19 cases, and history of COVID-19 illness. 3-5 mL of venous blood was collected from each participant and blood samples were tested using the Abbott SARS-CoV-2 IgG assay. Seroprevalence was estimated after applying the sampling weights and adjusting for clustering and assay characteristics. We randomly selected one adult serum sample from each household to compare the seroprevalence among adults between the two serosurveys. FINDINGS: Between Aug 18 and Sept 20, 2020, we enrolled and collected serum samples from 29 082 individuals from 15 613 households. The weighted and adjusted seroprevalence of SARS-CoV-2 IgG antibodies in individuals aged 10 years or older was 6·6% (95% CI 5·8-7·4). Among 15 084 randomly selected adults (one per household), the weighted and adjusted seroprevalence was 7·1% (6·2-8·2). Seroprevalence was similar across age groups, sexes, and occupations. Seroprevalence was highest in urban slum areas followed by urban non-slum and rural areas. We estimated a cumulative 74·3 million infections in the country by Aug 18, 2020, with 26-32 infections for every reported COVID-19 case. INTERPRETATION: Approximately one in 15 individuals aged 10 years or older in India had SARS-CoV-2 infection by Aug 18, 2020. The adult seroprevalence increased approximately tenfold between May and August, 2020. Lower infection-to-case ratio in August than in May reflects a substantial increase in testing across the country. FUNDING: Indian Council of Medical Research.

We conducted a nationally representative population-based survey in 60 districts from 15 Indian states covering all five geographic regions during 2017–2018 to estimate the age specific seroprevalence of dengue. Of the 12,300 sera collected, 4,955 were positive for IgG antibodies against dengue virus using IgG Indirect ELISA indicating past dengue infection. We tested 4,948 sera (seven had inadequate volume) positive for IgG antibodies on indirect ELISA using anti-dengue IgG capture ELISA to estimate the proportion of dengue infections with high antibody titers, suggestive of acute or recent secondary infection. Of the 4,948 sera tested, 529 (10.7%; 95% CI: 9.4–12.1) were seropositive on IgG capture ELISA. The proportions of dengue infections with high titers were 1.1% in the northeastern, 1.5% in the eastern, 6.2% in the western, 12.2% in the southern, and 16.7% in the northern region. The distribution of dengue infections varied across geographic regions, with a higher proportion of infections with high antibody titer in the northern and southern regions of India. The study findings could be useful for planning facilities for clinical management of dengue infections.

Introduction: India introduced a hepatitis-B (HB) vaccine in the Universal Immunization Program in 2002–2003 on a pilot basis, expanded to ten states in 2007–2008 (phase-1), and the entire country in 2011–2012 (phase-2). We tested sera from a nationally representative serosurvey conducted duing 2017, to estimate the seroprevalence of different markers of HB infection among children aged 5–17 years in India and to assess the impact of vaccination. Methods: We tested sera from 8273 children for different markers of HB infection and estimated weighted age-group specific seroprevalence of children who were chronically infected (HBsAg and anti-HBc positive), and immune due to past infection (anti-HBc positive and HBsAg negative), and having serological evidence of HB vaccination (only anti-HBs positive). We compared the prevalence of serological markers among children born before (aged 11–17 years) and after (aged 5-10 years) introduction of HB-vaccine from phase-1 states. Results: Among children aged 5–8 years, 1.1% were chronic carriers, 5.3% immune due to past infection, and 23.2% vaccinated. The corresponding proportions among children aged 9–17 years were 1.1%, 8.0%, and 12.0%, respectively. In phase-1 states, children aged 5–10 years had a significantly lower prevalence of anti-HBc (4.9% vs. 7.6%, p