Immunity against diphtheria among children aged 5 to17 years in India 2017 to 18 a cross sectional population based serosurvey

Globally, diphtheria was a leading cause of childhood morbidity and mortality in the pre-vaccination era. India contributes a substantial proportion of the global burden of diphtheria. Previous serological surveys helped to detect diphtheria resurgence, assess duration of immunity after vaccination, and guide strategies to reduce immunity gaps. However, they are underused in low- and middle-income countries. In India, very few seroepidemiological studies on diphtheria immunity exist. Existing studies mainly focus on adults, have small sample sizes. In this study, we used serum samples collected from children aged 5–17 years during a cross-sectional, population-based national serosurvey of dengue infection in India to estimate age-specific immunity against diphtheria.

The survey covered 5 regions of India (north, northeast, east, west, south) across all 30 states. Three states per region were randomly selected, and 4 districts per state were chosen using probability proportional to population size. From each district, 4 clusters (2 urban wards and 2 rural villages) were randomly selected, and one census enumeration block (CEB) per cluster was chosen. All households in each CEB (about 120–150 households) were enumerated through house-to-house visits using an Android app. From the listed population, 25 individuals were randomly selected from each age group (5–8, 9–17, 18–45 years). After consent, 3 mL blood samples were collected from participant for assessment of dengue infection. The survey collected 12,300 samples from 240 clusters in 60 districts across 15 states. This study used residual sera for estimating diphtheria immunity. For this study, only serum samples from children aged 5–17 years were included.