Abstract
Typhoid fever is estimated to cause between 11.9-26.9 million infections globally each year with 129,000-216,510 deaths. Access to improved water sources have reduced disease incidence in parts of the world but the use of efficacious vaccines is seen as an important public health tool for countries with a high disease burden. A new generation of Vi typhoid conjugate vaccines (TCVs), licensed for use in young children and expected to provide longer lasting protection than previous vaccines, are now available. The WHO Strategic Advisory Group of Experts on Immunization (SAGE) has convened a working group to review the evidence on TCVs and produce an updated WHO position paper for all typhoid vaccines in 2018 that will inform Gavi, the Vaccine Alliance's future vaccine investment strategies for TCVs. The Typhoid Vaccine Acceleration Consortium (TyVAC) has been formed through a $36.9 million funding program from the Bill & Melinda Gates Foundation to accelerate the introduction of TCVs into Gavi-eligible countries. In October 2016, a meeting was held to initiate planning of TCV effectiveness studies that will provide the data required by policy makers and stakeholders to support decisions on TCV use in countries with a high typhoid burden. Discussion topics included (1) the latest evidence and data gaps in typhoid epidemiology; (2) WHO and Gavi methods and data requirements; (3) data on TCV efficacy; (4) cost effectiveness analysis for TCVs from mathematical models; (5) TCV delivery and effectiveness study design. Specifically, participants were asked to comment on study design in 3 sites for which population-based typhoid surveillance is underway. The conclusion of the meeting was that country-level decision making would best be informed by the respective selected sites in Africa and Asia vaccinating children aged from 9-months to 15-years-old, employing either an individual or cluster randomized design with design influenced by population characteristics, transmission dynamics, and statistical considerations.
Highlights
Typhoid fever is estimated to cause between 11.9 million-26.9 million cases and 129,000–216,510 deaths annually [1,2,3]
A meeting of key stakeholders was held in Oxford, UK in October 2016 to discuss some of the critical issues surrounding typhoid fever and the impact on typhoid conjugate vaccines (TCV) effectiveness study design
An individually randomized trial could be used to determine the direct efficacy of TCVs in children under 2 years of age, which has been identified as a major knowledge gap
Summary
Typhoid fever is estimated to cause between 11.9 million-26.9 million cases and 129,000–216,510 deaths annually [1,2,3]. Two Vi tetanus toxoid conjugate vaccines have been licensed in India, with one manufacturer (Bharat Biotech) applying for WHO prequalification [12,13] Due to these developments, the WHO Strategic Advisory Group of Experts on Immunization (SAGE) has convened a working group to ‘review the scientific evidence and relevant programmatic considerations to formulate updated recommendations on the use of typhoid vaccines’ [14]. Publication of an updated WHO position paper on typhoid vaccines is scheduled for 2018 [14] These recommendations will be highly relevant to Gavi, given their prior positive statements on support for TCV. A meeting of key stakeholders was held in Oxford, UK in October 2016 to discuss some of the critical issues surrounding typhoid fever and the impact on TCV effectiveness study design
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