DONDENA Centre for Research on Social Dynamics, Università Commerciale L Bocconi, Milan, Italy.
DONDENA Centre for Research on Social Dynamics, Università Commerciale L Bocconi, Milan, Italy; Center for Information Technology, Bruno Kessler Foundation, Trento, Italy.
Lancet Infect Dis. 2017 Oct;17(10):1089-1097. doi: 10.1016/S1473-3099(17)30421-8. Epub 2017 Aug 11.
The persistent circulation of measles in both low-income and high-income countries requires a better characterisation of present epidemiological trends and existing immunity gaps across different sociodemographic settings. Serological surveys, which provide direct measures of population protection against the infection, are underexploited and often supply fragmentary estimates of population immunity. This study aims to investigate how measles immunity has changed over time across different socioeconomic settings, as a result of demographic changes and past immunisation policies.
For this multi-country modelling analysis, we developed a transmission model to simulate measles circulation during the past 65 years in nine countries with distinct demographic and vaccination histories. The model was calibrated on historical serological data and used to estimate the reduction of disease burden as a result of vaccination and present age-specific residual susceptibility.
Our model shows that estimated residual susceptibility to measles ranges from 3% in the UK to more than 10% in Kenya and Ethiopia. In high-income countries, such as Italy, Singapore, and South Korea, where routine first-dose administration produced more than 90% of immunised individuals, only about 20% of susceptible individuals are younger than 5 years. We also observed that the reduction in fertility that has occurred during the past decades in high-income countries has contributed to almost half of the reduction in measles incidence. In low-income countries, where fertility is high, the population is younger and routine vaccination has been suboptimum. Susceptible individuals are concentrated in early childhood, with about 60% of susceptible individuals in Ethiopia younger than 10 years. In these countries, Supplementary Immunization Activities (SIAs) were responsible for more than 25% of immunised individuals (up to 45% in Ethiopia), mitigating the consequences of suboptimum routine vaccination coverage.
Future vaccination strategies in high-fertility countries should focus on increasing childhood immunisation rates, either by raising first-dose coverage or by making erratic SIAs more frequent and regular. Immunisation campaigns targeting adolescents and adults are required in low-fertility countries, where the susceptibility in these age groups will otherwise sustain measles circulation.
European Research Council.
麻疹在低收入和高收入国家持续传播，这要求我们更好地描述不同社会人口环境下当前的流行病学趋势和现有的免疫差距。血清学调查提供了人群对感染的直接保护措施，但该方法未得到充分利用，且常常提供不完整的人群免疫估计。本研究旨在调查由于人口变化和过去的免疫政策，不同社会经济环境下麻疹免疫力是如何随时间变化的。
在这项多国建模分析中，我们开发了一个传播模型，以模拟过去 65 年中 9 个具有不同人口统计学和疫苗接种历史的国家的麻疹传播情况。该模型根据历史血清学数据进行校准，并用于估计疫苗接种带来的疾病负担减少情况，以及目前特定年龄组的剩余易感性。
我们的模型表明，估计的麻疹剩余易感性范围从英国的 3%到肯尼亚和埃塞俄比亚的 10%以上。在意大利、新加坡和韩国等高收入国家，常规接种第一剂疫苗使 90%以上的人群免疫，只有约 20%的易感人群年龄小于 5 岁。我们还观察到，过去几十年中高收入国家生育率的下降，导致麻疹发病率下降了近一半。在生育率较高的低收入国家，人口更年轻，常规疫苗接种效果不佳。易感人群集中在幼儿期，埃塞俄比亚约有 60%的易感人群年龄小于 10 岁。在这些国家，补充免疫活动（SIAs）为超过 25%的人群（在埃塞俄比亚高达 45%）提供了免疫，减轻了常规疫苗接种覆盖率不足的后果。
高生育率国家的未来疫苗接种策略应侧重于提高儿童免疫率，无论是通过提高第一剂覆盖率，还是通过更频繁、更有规律地开展不规则的 SIAs。在低生育率国家，需要针对青少年和成年人开展免疫接种运动，否则这些年龄组的易感性将持续维持麻疹的传播。
欧洲研究理事会。
