Targeting vaccinations for the licensed dengue vaccine: considerations for serosurvey design

Background The CYD-TDV vaccine was unusual in that the recommended target population for vaccination was originally defined not only by age, but also by transmission setting as defined by seroprevalence. WHO originally recommended countries consider vaccination against dengue with CYD-TDV vaccine in geographic settings only where prior infection with any dengue serotype, as measured by seroprevalence, was >170% in the target age group. Vaccine was not recommended in settings where seroprevalence was <50%. Test-and-vaccinate strategies suggested following new analysis by Sanofi will still require age-stratified seroprevalence surveys to optimise age-group targeting. Here we address considerations for serosurvey design in the context of vaccination program planning. Methods To explore how the design of seroprevalence surveys affects estimates of transmission intensity, 100 age-specific seroprevalence surveys were simulated using a beta-binomial distribution and a simple catalytic model for different combinations of age-range, survey size, transmission setting, and test sensitivity/specificity. We then used a Metropolis-Hastings Markov Chain Monte-Carlo algorithm to estimate the force of infection from each simulated dataset. Results Sampling from a wide age-range led to more accurate estimates than merely increasing sample size in a narrow age-range. This finding was consistent across all transmission settings. The optimum test sensitivity and specificity given an imperfect test differed by setting with high sensitivity being important in high transmission settings and high specificity important in low transmission settings. Conclusions When assessing vaccination suitability by seroprevalence surveys, countries should ensure an appropriate age-range is sampled, considering epidemiological evidence about the local burden of disease

The importance of effective risk communication and transparency: lessons from the dengue vaccine controversy in the Philippines

In 2016 the Philippine Department of Health (DOH) introduced a novel dengue vaccine in a mass immunization program to reduce the substantial economic and social burden of the disease on households and the government. The vaccine manufacturer’s announcement regarding new findings on the small but increased risk of severe dengue for vaccinated seronegative patients caused turmoil as various people claimed that the vaccine caused deaths and that health authorities are corrupt. While health department staff split—some having to preserve its reputation and others to monitor over 800,000 children administered the vaccine—communication between the frontline health workers and parents suffered. As a result, public confidence in vaccines dramatically dropped and the repercussions challenge the public health system. We examine factors that contributed to the crisis and argue for strengthening risk communication strategies and increasing transparency on decision making to counter misinformation and protect public health