Department of Statistics, University of Oxford, 24-29 St Giles', Oxford OX1 3LB, UK.
Department of Statistics, University of Oxford, 24-29 St Giles', Oxford OX1 3LB, UK; MRC Centre for Global Infectious Disease Analysis, Imperial College London, St. Mary's Campus, Norfolk Place, London W2 1PG, UK.
Vaccine. 2021 Dec 3;39(49):7182-7190. doi: 10.1016/j.vaccine.2021.10.001. Epub 2021 Oct 20.
Between September 2017 and June 2019, an outbreak of hepatitis A virus (HAV) occurred in Louisville, Kentucky, resulting in 501 cases and 6 deaths, predominantly among persons who experience homelessness or who use drugs (PEH/PWUD). The critical vaccination threshold (V) required to achieve herd immunity in this population is unknown. We investigated V and vaccination impact using epidemic modeling.
To determine which population subgroups had high infection risks, we employed a technique based on comparing the proportion of cases arising before and after the epidemic peak, across subgroups. We also developed a dynamic deterministic model of HAV transmission among PEH/PWUD to estimate the basic reproduction number (R), herd immunity threshold, V and the effect of timing of the vaccination intervention on epidemic and economic outcomes.
Of the 501 confirmed or probable cases, 385 (76.8%) were among PEH/PWUD. Among PEH/PWUD and within the general population, homelessness was a significant risk factor for infection in the initial stages of the outbreak (odds ratios for homeless versus not homeless: 2.62; 95% confidence interval (CI): 1.62-4.25 for PEH/PWUD and 2.39; 95% CI: 1.51-3.78 for all detected cases). Our estimate for R ranges between 2.85 and 3.54, corresponding to an estimate of 69% (95% CI: 65-72) for herd immunity threshold and 76% (95% CI: 72%-80%) for V assuming a vaccine with 90% efficacy. The observed vaccination program was estimated to have averted 30 hospitalizations (95% CI: 19-43), associated with over US$490 000 (95% CI: $310 000-700 000) in hospitalization cost. Greater impact was observed with earlier and faster vaccination implementation.
Vaccination coverage of at least 77% is likely required to prevent outbreaks of HAV among PEH/PWUD in Louisville, assuming a 90% vaccine efficacy. Proactive hepatitis A vaccination programs among PEH/PWUD will maximize health and economic benefits of these programs and reduce the likelihood of another outbreak.
2017 年 9 月至 2019 年 6 月期间，肯塔基州路易斯维尔市爆发了甲型肝炎病毒（HAV）疫情，导致 501 例病例和 6 例死亡，主要发生在无家可归者或吸毒者（PEH/PWUD）中。在该人群中实现群体免疫所需的关键疫苗接种阈值（V）尚不清楚。我们使用流行性病学模型研究了 V 和疫苗接种的影响。
为了确定哪些人群亚组具有较高的感染风险，我们采用了一种技术，该技术基于比较流行高峰期前后各亚组中病例的比例来确定。我们还开发了一种针对 PEH/PWUD 中 HAV 传播的动态确定性模型，以估计基本繁殖数（R）、群体免疫阈值、V 以及疫苗接种干预时机对疫情和经济结果的影响。
在 501 例确诊或疑似病例中，385 例（76.8%）发生在 PEH/PWUD 中。在 PEH/PWUD 和一般人群中，无家可归是疫情初期感染的一个重要危险因素（与无家可归者相比，无家可归者的比值比为 2.62；95%置信区间（CI）为 1.62-4.25；所有检测到的病例）。我们对 R 的估计范围在 2.85 到 3.54 之间，这对应于群体免疫阈值为 69%（95%CI：65-72%）和疫苗接种率为 76%（95%CI：72%-80%）的估计值，假设疫苗的有效性为 90%。观察到的疫苗接种计划估计可避免 30 例住院治疗（95%CI：19-43），与超过 49 万美元（95%CI：31 万至 70 万美元）的住院费用相关。更早和更快的疫苗接种实施将产生更大的影响。
假设疫苗有效性为 90%，那么路易斯维尔市的 PEH/PWUD 中预防 HAV 爆发可能需要至少 77%的疫苗接种覆盖率。针对 PEH/PWUD 的主动甲型肝炎疫苗接种计划将最大限度地提高这些计划的健康和经济效益，并降低再次爆发的可能性。
