Public Health Ontario, Toronto, ON, Canada.
Public Health Ontario, Toronto, ON, Canada; Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada.
Lancet Infect Dis. 2017 Dec;17(12):e420-e428. doi: 10.1016/S1473-3099(17)30307-9. Epub 2017 Jul 27.
The basic reproduction number, R nought (R), is defined as the average number of secondary cases of an infectious disease arising from a typical case in a totally susceptible population, and can be estimated in populations if pre-existing immunity can be accounted for in the calculation. R determines the herd immunity threshold and therefore the immunisation coverage required to achieve elimination of an infectious disease. As R increases, higher immunisation coverage is required to achieve herd immunity. In July, 2010, a panel of experts convened by WHO concluded that measles can and should be eradicated. Despite the existence of an effective vaccine, regions have had varying success in measles control, in part because measles is one of the most contagious infections. For measles, R is often cited to be 12-18, which means that each person with measles would, on average, infect 12-18 other people in a totally susceptible population. We did a systematic review to find studies reporting rigorous estimates and determinants of measles R. Studies were included if they were a primary source of R, addressed pre-existing immunity, and accounted for pre-existing immunity in their calculation of R. A search of key databases was done in January, 2015, and repeated in November, 2016, and yielded 10 883 unique citations. After screening for relevancy and quality, 18 studies met inclusion criteria, providing 58 R estimates. We calculated median measles R values stratified by key covariates. We found that R estimates vary more than the often cited range of 12-18. Our results highlight the importance of countries calculating R using locally derived data or, if this is not possible, using parameter estimates from similar settings. Additional data and agreed review methods are needed to strengthen the evidence base for measles elimination modelling.
基本繁殖数，R0（R），定义为在完全易感人群中，典型病例引起的继发病例的平均数量，并且可以在人群中进行估计，如果可以在计算中考虑到预先存在的免疫力。R 确定了群体免疫阈值，因此需要免疫接种覆盖率来实现消除传染病。随着 R 的增加，需要更高的免疫接种覆盖率来实现群体免疫。2010 年 7 月，世界卫生组织召集的一个专家组得出结论，麻疹可以而且应该被消灭。尽管存在有效的疫苗，但各地区在麻疹控制方面取得的成功程度不同，部分原因是麻疹是最具传染性的感染之一。对于麻疹，R 通常被引用为 12-18，这意味着每个麻疹患者平均会在完全易感人群中感染 12-18 人。我们进行了系统评价，以找到报告严格估计麻疹 R 值及其决定因素的研究。如果研究是 R 的主要来源，解决了预先存在的免疫力问题，并在计算 R 时考虑到了预先存在的免疫力，则将其纳入研究。2015 年 1 月和 2016 年 11 月进行了关键数据库的搜索，并产生了 10 883 个独特的引文。经过相关性和质量筛选，有 18 项研究符合纳入标准，提供了 58 个 R 估计值。我们按关键协变量对麻疹 R 值进行了分层计算中位数。我们发现，R 估计值的变化比通常引用的 12-18 范围大得多。我们的研究结果强调了各国使用本地数据计算 R 的重要性，或者如果这不可能，则使用类似环境的参数估计值。需要更多的数据和商定的审查方法来加强麻疹消除建模的证据基础。
