Department of Epidemiology of Microbial Diseases, Yale School of Public Health, 60 College St., P.O. Box 208034, New Haven, CT, 06520-8034, USA.
Swiss Tropical and Public Health Institute, Basel, Switzerland.
BMC Infect Dis. 2023 Mar 8;23(1):143. doi: 10.1186/s12879-023-08105-2.
Several prolonged typhoid fever epidemics have been reported since 2010 throughout eastern and southern Africa, including Malawi, caused by multidrug-resistant Salmonella Typhi. The World Health Organization recommends the use of typhoid conjugate vaccines (TCVs) in outbreak settings; however, current data are limited on how and when TCVs might be introduced in response to outbreaks.
We developed a stochastic model of typhoid transmission fitted to data from Queen Elizabeth Central Hospital in Blantyre, Malawi from January 1996 to February 2015. We used the model to evaluate the cost-effectiveness of vaccination strategies over a 10-year time horizon in three scenarios: (1) when an outbreak is likely to occur; (2) when an outbreak is unlikely to occur within the next ten years; and (3) when an outbreak has already occurred and is unlikely to occur again. We considered three vaccination strategies compared to the status quo of no vaccination: (a) preventative routine vaccination at 9 months of age; (b) preventative routine vaccination plus a catch-up campaign to 15 years of age; and (c) reactive vaccination with a catch-up campaign to age 15 (for Scenario 1). We also explored variations in outbreak definitions, delays in implementation of reactive vaccination, and the timing of preventive vaccination relative to the outbreak.
Assuming an outbreak occurs within 10 years, we estimated that the various vaccination strategies would prevent a median of 15-60% of disability-adjusted life-years (DALYs). Reactive vaccination was the preferred strategy for WTP values of $0-300 per DALY averted. For WTP values > $300, introduction of preventative routine TCV immunization with a catch-up campaign was the preferred strategy. Routine vaccination with a catch-up campaign was cost-effective for WTP values above $890 per DALY averted if no outbreak occurs and > $140 per DALY averted if implemented after the outbreak has already occurred.
Countries for which the spread of antimicrobial resistance is likely to lead to outbreaks of typhoid fever should consider TCV introduction. Reactive vaccination can be a cost-effective strategy, but only if delays in vaccine deployment are minimal; otherwise, introduction of preventive routine immunization with a catch-up campaign is the preferred strategy.
自 2010 年以来，东非和南非多个国家报告了多起持续性伤寒疫情，包括马拉维，这些疫情由耐多药伤寒沙门氏菌引起。世界卫生组织建议在疫情爆发时使用伤寒结合疫苗（TCV）；然而，目前关于 TCV 如何以及何时可能针对疫情爆发而引入的数据有限。
我们开发了一个伤寒传播的随机模型，该模型拟合了马拉维布兰太尔伊丽莎白女王中央医院 1996 年 1 月至 2015 年 2 月的数据。我们使用该模型在三种情况下评估了未来十年内疫苗接种策略的成本效益：（1）可能发生疫情时；（2）未来十年内不太可能发生疫情时；（3）已经发生疫情且不太可能再次发生时。我们考虑了三种与不接种疫苗的现状相比的疫苗接种策略：（a）9 个月龄时进行预防性常规接种；（b）9 个月龄时进行预防性常规接种，以及 15 岁时进行补种运动；（c）在发生疫情时进行反应性疫苗接种，以及 15 岁时进行补种运动（适用于情景 1）。我们还探讨了疫情定义的变化、反应性疫苗接种实施的延迟以及预防性疫苗接种相对于疫情的时间安排。
假设疫情在 10 年内发生，我们估计各种疫苗接种策略将预防 15-60%的残疾调整生命年（DALY）。对于支付意愿值为 0-300 美元的 DALY 来说，反应性疫苗接种是首选策略。对于支付意愿值大于 300 美元的情况，引入带有补种运动的预防性常规 TCV 免疫接种是首选策略。如果没有疫情发生，带有补种运动的常规疫苗接种每预防 1 个 DALY 的成本效益超过 890 美元，如果在疫情发生后实施，则每预防 1 个 DALY 的成本效益超过 140 美元。
对于那些由于抗生素耐药性传播可能导致伤寒爆发的国家，应考虑引入 TCV。反应性疫苗接种可以是一种具有成本效益的策略，但前提是疫苗接种的延迟最小；否则，引入带有补种运动的预防性常规免疫接种是首选策略。
