Forecasting Demand for the Typhoid Conjugate Vaccine in Low- and Middle-income Countries.

Frédéric Debellut,Dagna Constenla,Kathleen M Neuzil,Clint Pecenka,Virginia E Pitzer,Nathaniel Hendrix,Anthony Marfin,Naor Bar-Zeev

doi:10.1093/cid/ciy1076

Abstract

BackgroundThe World Health Organization (WHO) released a position paper in March 2018 calling for integration of a novel typhoid conjugate vaccine (TCV) into routine immunization along with catch-up campaigns for children up to age 15. Gavi, the Vaccine Alliance, has committed funding to help resource-constrained countries introduce this vaccine. In this article, the Typhoid Vaccine Acceleration Consortium forecasts demand if WHO recommendations are followed.MethodsWe built a model of global TCV introductions between 2020 and 2040 to estimate the demand of the vaccine for 133 countries. We estimated each country’s year of introduction by examining its estimated incidence of typhoid fever, its history of introducing new vaccines, and any knowledge we have of its engagement with typhoid prevention, including intention to apply for Gavi funding. Our model predicted use in routine infant vaccination as well as campaigns targeting varying proportions of the unvaccinated population up to 15 years of age.ResultsBetween 2020 and 2025, demand will predominantly come from African countries, many receiving Gavi support. After that, Asian countries generate most demand until 2030, when campaigns are estimated to end. Demand will then track the birth cohort of participating countries, suggesting an annual routine demand between 90 and 100 million doses. Peak demand is likely to occur between 2023 and 2026, approaching 300 million annual doses if campaign implementation is high.ConclusionsIn our analysis, target population for catch-up campaigns is the main driver of uncertainty. At peak demand, there is some risk of exceeding presently estimated peak production capacity. Therefore, it will be important to carefully coordinate introductions, especially when accompanied by campaigns targeting large proportions of the eligible population.

Highlights

The World Health Organization (WHO) released a position paper in March 2018 calling for integration of a novel typhoid conjugate vaccine (TCV) into routine immunization along with catch-up campaigns for children up to age 15
Global typhoid burden has fallen since the 1990s, incidence appears stable over the past few years [1], and antimicrobials have lowered mortality associated with typhoid fever
Because TCV is the first typhoid vaccine eligible to be added to the Expanded Program on Immunization (EPI) schedule, we anticipate that vaccination of 9-month-old infants will form the basis of most countries’ introduction strategies

Summary

Methods

We built a model of global TCV introductions between 2020 and 2040 to estimate the demand of the vaccine for 133 countries. Our model predicted use in routine infant vaccination as well as campaigns targeting varying proportions of the unvaccinated population up to 15 years of age. WHO recommends that introduction in EPI be accompanied by a catch-up campaign to vaccinate all children 15 years of age and younger who did not receive TCV in infancy. As this campaign may target all members of this age cohort or only those considered high risk, we examine 6 scenarios with target cohorts for the catch-up campaigns ranging from 0% to 100% of the eligible population. The model calculates the number of TCV doses distributed in both routine and campaign administration settings while adjusting for 2 additional sources of demand: wastage due to expiration or spoilage; and buffer stock, which is a 1-time purchase of extra vaccine meant to support continued use in case of supply disruptions.

Results

Discussion

Conclusion