Yale School of Public Health, Yale University, New Haven, CT, USA.
Yale School of Public Health, Yale University, New Haven, CT, USA; Swiss Tropical and Public Health Institute, Allschwil, Switzerland; University of Basel, Basel, Switzerland.
Vaccine. 2023 Jan 23;41(4):965-975. doi: 10.1016/j.vaccine.2022.12.032. Epub 2022 Dec 29.
Models are useful to inform policy decisions on typhoid conjugate vaccine (TCV) deployment in endemic settings. However, methodological choices can influence model-predicted outcomes. To provide robust estimates for the potential public health impact of TCVs that account for structural model differences, we compared four dynamic and one static mathematical model of typhoid transmission and vaccine impact. All models were fitted to a common dataset of age-specific typhoid fever cases in Kolkata, India. We evaluated three TCV strategies: no vaccination, routine vaccination at 9 months of age, and routine vaccination at 9 months with a one-time catch-up campaign (ages 9 months to 15 years). The primary outcome was the predicted percent reduction in symptomatic typhoid cases over 10 years after vaccine introduction. For three models with economic analyses (Models A-C), we also compared the incremental cost-effectiveness ratios (ICERs), calculated as the incremental cost (US$) per disability-adjusted life-year (DALY) averted. Routine vaccination was predicted to reduce symptomatic cases by 10-46 % over a 10-year time horizon under an optimistic scenario (95 % initial vaccine efficacy and 19-year mean duration of protection), and by 2-16 % under a pessimistic scenario (82 % initial efficacy and 6-year mean protection). Adding a catch-up campaign predicted a reduction in incidence of 36-90 % and 6-35 % in the optimistic and pessimistic scenarios, respectively. Vaccine impact was predicted to decrease as the relative contribution of chronic carriers to transmission increased. Models A-C all predicted routine vaccination with or without a catch-up campaign to be cost-effective compared to no vaccination, with ICERs varying from $95-789 per DALY averted; two models predicted the ICER of routine vaccination alone to be greater than with the addition of catch-up campaign. Despite differences in model-predicted vaccine impact and cost-effectiveness, routine vaccination plus a catch-up campaign is likely to be impactful and cost-effective in high incidence settings such as Kolkata.
模型可用于为在流行地区部署伤寒结合疫苗（TCV）的决策提供信息。然而，方法选择会影响模型预测的结果。为了提供针对 TCV 的潜在公共卫生影响的稳健估计，这些 TCV 考虑了结构模型差异，我们比较了四种动态和一种静态伤寒传播和疫苗影响的数学模型。所有模型都使用印度加尔各答的年龄特异性伤寒病例的共同数据集进行拟合。我们评估了三种 TCV 策略：不接种疫苗、在 9 个月龄时常规接种疫苗，以及在 9 个月龄时进行一次补充接种（9 个月至 15 岁）。主要结果是预测在疫苗引入后 10 年内症状性伤寒病例的百分比减少。对于具有经济分析的三个模型（模型 A-C），我们还比较了增量成本效益比（ICER），计算方法为每避免一个残疾调整生命年（DALY）的增量成本（美元）。在乐观情况下（95%的初始疫苗效力和 19 年的平均保护期），10 年时间内常规接种疫苗预计可减少 10-46%的症状性病例，在悲观情况下（82%的初始效力和 6 年的平均保护期），减少 2-16%。接种补充疫苗预计可使发病率降低 36-90%和 6-35%，分别在乐观和悲观情况下。疫苗的影响预计会随着慢性携带者对传播的相对贡献增加而降低。模型 A-C 均预测，无论是否接种补充疫苗，常规接种疫苗均具有成本效益，与不接种疫苗相比，ICER 从每避免一个 DALY 的 95 美元到 789 美元不等；两个模型预测单独接种常规疫苗的 ICER 大于接种补充疫苗。尽管模型预测的疫苗影响和成本效益存在差异，但在像加尔各答这样发病率高的地区，常规接种疫苗加补充疫苗可能具有影响力且具有成本效益。
