Dengue vaccine supplies under endemic and epidemic conditions in three dengue-endemic countries: Colombia, Thailand, and Vietnam.

BACKGROUND: Dengue fever has been a major public health concern in Colombia, Thailand, and Vietnam. Unlike other infectious diseases, dengue vaccines had not been available for a long time, causing difficulties to control the disease. However, the first live attenuated, tetravalent dengue vaccine (CYD-TDV) became available in 2016 and has been already licensed in some dengue-endemic countries. Because several second-generation dengue vaccines are also in the pipeline, it is critical to understand the efficient allocation of dengue vaccines considering the geographical variation of the disease.

METHODS: The Climate Risk Factor (CRF) index was created using the climate and non-climate factors in the three countries. A random-coefficient negative binomial model was chosen to validate the relationship between the CRF index and dengue incidence proxy. Given the statistical significance of the CRF index, high risk areas for dengue fever were identified at the 5 km by 5 km resolution and used to estimate vaccination coverage rates and the number of doses required for various types of vaccination scenarios by country.

RESULTS AND CONCLUSIONS: Based upon a three-dose scheme, the estimated number of vaccines required for routine vaccination targeting 9 years old ranged from 1 to 2.6 million doses across the countries during the first year of introduction. A one-off catch-up campaign targeting the age group of 10-17 year olds would require 8 to 18 million additional doses. Routine vaccination (with or without a catch-up campaign) covered 63%, 90%, and 91% of the targeted age group populations in Colombia, Thailand, and Vietnam respectively. Given that many dengue-endemic countries face limited resources and that the costs for mass vaccination campaigns may not be trivial, the findings of this study can guide the decision makers in the three countries regarding the efficient distribution of vaccines by identifying populations at high risk at 5 km by 5 km resolution.