China-Australia Joint Research Centre for Infectious Diseases, School of Public Health, Xi'an Jiaotong University Health Science Center, Xi'an, Shaanxi, PR China; Key Laboratory for Disease Prevention and Control and Health Promotion of Shaanxi Province, Xi'an, Shaanxi, PR China.
Jiangsu Provincial Center for Diseases Control and Prevention, Nanjing, Jiangsu 210009, PR China.
J Theor Biol. 2022 Nov 7;551-552:111242. doi: 10.1016/j.jtbi.2022.111242. Epub 2022 Aug 8.
Measles has re-emerged globally due to the accumulation of susceptible individuals and immunity gap, which causes challenges in eliminating measles. Routine vaccination and supplementary immunization activities (SIAs) have greatly improved measles control, but the impact of SIAs on the measles transmission dynamics remains unclear as the vaccine-induced immunity wanes.
We developed a comprehensive measles transmission dynamics model by taking into account population demographics, age-specific contact patterns, seasonality, routine vaccination, SIAs, and the waning vaccine-induced immunity. The model was calibrated by the monthly age-specific cases data from 2005 to 2018 in Jiangsu Province, China, and validated by the dynamic sero-prevalence data. We aimed to investigate the short-term and long-term impact of three-time SIAs during 2009-2012 (9.68 million and 4.25 million children aged 8 months-14 years in March 2009 and September 2010, respectively, and 140,000 children aged 8 months-6 years in March 2012) on the measles disease burden and explored whether additional SIAs could accelerate the measles elimination.
We estimated that the cumulative numbers of measles cases from March 2009 to December 2012 (in the short run) and to December 2018 (in the long run) after three-time SIAs (base case) were 6,699 (95% confidence interval [CI]: 2,928-10,469), and 22,411 (15,146-29,675), which averted 45.0% (42.9%-47.0%) and 34.3% (30.7%-37.9%) of 12,226 (4,916-19,537) and 34,274 (21,350-47,199) cases without SIAs, respectively. The fraction of susceptibles for children aged 8-23 months and 2-14 years decreased from 8.3% and 10.8% in March 2009 to 5.8% and 5.8% in April 2012, respectively. However, the fraction of susceptibles aged 15-49 years and above 50 years increased gradually to about 15% in 2018 irrespective of SIAs due to the waning immunity. The measles elimination goal would be reached in 2028, and administrating additional one-off SIAs in September 2022 to children aged 8-23 months, or young adolescents aged 15-19 years could accelerate the elimination one year earlier.
SIAs have greatly reduced the measles incidence and the fraction of susceptibles, but the benefit may wane over time. Under the current interventions, Jiangsu province would reach the measles elimination goal in 2028. Additional SIAs may accelerate the measles elimination one year earlier.
由于易感人群的积累和免疫差距，麻疹在全球范围内再次出现，这给消除麻疹带来了挑战。常规疫苗接种和补充免疫活动（SIAs）极大地改善了麻疹控制，但由于疫苗诱导的免疫力下降，SIAs 对麻疹传播动力学的影响仍不清楚。
我们考虑了人口统计学、特定年龄的接触模式、季节性、常规疫苗接种、SIAs 和疫苗诱导免疫力的衰减，开发了一个全面的麻疹传播动力学模型。该模型通过中国江苏省 2005 年至 2018 年每月特定年龄的病例数据进行校准，并通过动态血清流行率数据进行验证。我们旨在研究 2009-2012 年三次 SIA（2009 年 3 月和 2010 年 9 月为 8 个月至 14 岁的 968 万儿童，以及 2012 年 3 月为 8 个月至 6 岁的 14 万儿童）对麻疹疾病负担的短期和长期影响，并探讨是否可以通过额外的 SIA 来加速麻疹消除。
我们估计，在三次 SIA 后（基础情况），从 2009 年 3 月至 2012 年 12 月（短期）和 2018 年 12 月（长期），麻疹累计病例数为 6699（95%置信区间[CI]：2928-10469）和 22411（15146-29675），与无 SIA 情况下的 12226（4916-19537）和 34274（21350-47199）相比，分别避免了 45.0%（42.9%-47.0%）和 34.3%（30.7%-37.9%）的病例。8-23 个月和 2-14 岁儿童的易感人群比例从 2009 年 3 月的 8.3%和 10.8%分别下降到 2012 年 4 月的 5.8%和 5.8%。然而，由于免疫力下降，15-49 岁和 50 岁以上人群的易感人群比例逐渐增加，到 2018 年约为 15%。无论是否进行 SIA，江苏省都将在 2028 年达到消除麻疹的目标，在 2022 年 9 月对 8-23 个月大的儿童或 15-19 岁的青少年进行一次性额外 SIA，可以将消除麻疹的目标提前一年实现。
SIAs 大大降低了麻疹的发病率和易感人群比例，但随着时间的推移，其益处可能会减弱。在当前的干预措施下，江苏省将在 2028 年达到消除麻疹的目标。额外的 SIA 可能会提前一年实现麻疹的消除。
