Medical Research Council Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London W2 1PG, United Kingdom;
Regional Office for Europe, World Health Organization, DK-2100 Copenhagen, Denmark;Global Immunization Division, Center for Global Health, Centers for Disease Control and Prevention, Atlanta, GA 30333;
Proc Natl Acad Sci U S A. 2014 Jul 22;111(29):10604-9. doi: 10.1073/pnas.1323688111. Epub 2014 Jul 7.
As polio eradication inches closer, the absence of poliovirus circulation in most of the world and imperfect vaccination coverage are resulting in immunity gaps and polio outbreaks affecting adults. Furthermore, imperfect, waning intestinal immunity among older children and adults permits reinfection and poliovirus shedding, prompting calls to extend the age range of vaccination campaigns even in the absence of cases in these age groups. The success of such a strategy depends on the contribution to poliovirus transmission by older ages, which has not previously been estimated. We fit a mathematical model of poliovirus transmission to time series data from two large outbreaks that affected adults (Tajikistan 2010, Republic of Congo 2010) using maximum-likelihood estimation based on iterated particle-filtering methods. In Tajikistan, the contribution of unvaccinated older children and adults to transmission was minimal despite a significant number of cases in these age groups [reproduction number, R = 0.46 (95% confidence interval, 0.42-0.52) for >5-y-olds compared to 2.18 (2.06-2.45) for 0- to 5-y-olds]. In contrast, in the Republic of Congo, the contribution of older children and adults was significant [R = 1.85 (1.83-4.00)], perhaps reflecting sanitary and socioeconomic variables favoring efficient virus transmission. In neither setting was there evidence for a significant role of imperfect intestinal immunity in the transmission of poliovirus. Bringing the immunization response to the Tajikistan outbreak forward by 2 wk would have prevented an additional 130 cases (21%), highlighting the importance of early outbreak detection and response.
随着根除脊髓灰质炎工作的推进，世界上大多数地区已不再有脊灰病毒循环，而疫苗接种覆盖率存在缺陷，这导致免疫空白和脊灰暴发影响到成年人。此外，大龄儿童和成年人肠道免疫力不完善、逐渐减弱，会导致再次感染和脊灰病毒排出，因此即使在这些年龄组没有病例的情况下，也有人呼吁扩大疫苗接种活动的年龄范围。这种策略的成功取决于大龄人群对脊灰病毒传播的贡献，而此前尚未对此进行估计。我们利用迭代粒子滤波法基于最大似然估计，将脊灰病毒传播的数学模型拟合到两个影响成年人的大型暴发（2010 年塔吉克斯坦和 2010 年刚果共和国）的时间序列数据，对大龄人群在传播中的贡献进行了估计。在塔吉克斯坦，尽管这些年龄组有大量病例，但未接种疫苗的大龄儿童和成年人对传播的贡献微不足道[>5 岁人群的繁殖数 R 为 0.46（95%置信区间，0.42-0.52），而 0-5 岁人群的 R 为 2.18（2.06-2.45）]。相比之下，在刚果共和国，大龄儿童和成年人的贡献是显著的[R = 1.85（1.83-4.00）]，这可能反映了有利于病毒高效传播的卫生和社会经济变量。在这两种情况下，都没有证据表明不完善的肠道免疫力在脊灰病毒传播中发挥了重要作用。如果将塔吉克斯坦暴发的免疫应对提前 2 周，将可预防另外 130 例（21%）病例，这突显了早期暴发检测和应对的重要性。
