Developing Country Vaccination Recommendations for Travellers: The UK National Travel Health Network and Centre (NaTHNaC) Methodology for Typhoid and Hepatitis A

Abstract Background The National Travel Health Network and Centre (NaTHNaC) regularly reviews country-specific vaccination recommendations to align with current epidemiological evidence. This update aimed to refine hepatitis A and typhoid vaccination guidance by integrating recent data and clarifying decision-making criteria. Methods A structured review of hepatitis A and typhoid epidemiology (2022-2025) used Global Burden of Disease data, World Bank income classifications, and Age at Midpoint of Population Immunity values to assess hepatitis A endemicity. Typhoid risk was categorised using incidence thresholds defining high, intermediate, and low risk. National income level served as a proxy for sanitation, while antimicrobial resistance informed recommendations. Extensively drug-resistant typhoid prompted vaccination recommendations for most travellers regardless of incidence. Where data were limited, previous NaTHNaC guidance, UK Health Security Agency information, outbreak reports, and expert consensus were used. Epidemiologically borderline countries underwent individual review, and recommendations were validated before publication. Results Hepatitis A recommendations were based on endemicity, incidence, and income status. High endemicity or incidence generally warranted vaccination for most travellers, whereas low endemicity in high-income countries usually did not. Thirty recommendation updates were introduced, affecting 15.4% of countries worldwide (30/195), mainly in Central Asia and the Caribbean. Several high-income countries, including Israel and Panama, were reclassified to lower risk, although vaccination remains recommended for certain travellers to countries such as South Korea and Chile because of recurrent outbreaks. Typhoid guidance incorporated incidence, income level, and antimicrobial resistance patterns. Forty recommendation updates were made, affecting 20.5% of countries worldwide (40/195). Changes included lower-risk classifications across much of the Americas and increased-risk classifications in parts of the Middle East, Eastern Europe, and Oceania. Conclusions These revisions strengthen evidence-based travel health advice and highlight the need for continued adaptation of vaccination policies. However, limitations in surveillance and modelling data, including incomplete reporting and potential bias propagation, emphasise the need for improved global infectious disease monitoring.