Abstract
A mathematical model of dengue transmission was developed to estimate the impact of dengue vaccination. It was first fitted to the empirical dengue seroprevalence data from Rayong province of Thailand in order to reproduce the epidemiology observed without vaccination. The deterministic age-structured compartmental model included explicit host and vector populations, seasonality, all four dengue serotypes and interactions between them. To fit the model to the empirical data, twenty-five calibration scenarios were determined. Each scenario was a combination of cross-protection duration and an increase in susceptibility following the primary infection. For each combination, the probability of virus transmission was estimated by fitting the model to the seroprevalence collected in children aged 6 to 18 in Rayong. Incidence curves predicted with each combination were visually assessed and compared to the reported incidence corrected for under-reporting. Scenarios with good fit to seroprevalence data and realistic incidence curves were characterised by high values of susceptibility enhancement (4- to 9-fold increases in susceptibility following primary infection) and cross-protection duration. A high susceptibility enhancement factor was required for the model to predict comparable prevalence of multiple dengue infections. The modelled prevalence was close to observed values for almost all age groups, although lower for children aged 6 to 7 by up to 10 percentage points. Scenarios with higher susceptibility enhancement and cross-protection predicted greater fluctuations in annual dengue incidence, in line with observed data (corrected for under-reporting). Several scenarios allowed fitting the model to the empirical data from Rayong province. The inclusion of susceptibility enhancement considerably improved the fit to seroprevalence data. Higher enhancement factors in combination with longer cross-protection duration also led to more realistic incidence patterns. The validated scenarios reproduced empirical dengue incidence in the Rayong province, which is a preliminary condition for analyses of vaccination impact scenarios.
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