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The impact of supplementary immunization activities on measles transmission dynamics and implications for measles
Mingwang Shen1, Xiang Sun2, Yanni Xiao3
1China-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.
Background:
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.
Methods:
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.
Results:
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.
Conclusions:
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.
Insights
Supplementary immunization activities (SIAs) significantly reduced measles cases, but waning immunity necessitates ongoing efforts. Additional SIAs could accelerate measles elimination by one year, reaching the goal sooner.
Area of Science:
- Epidemiology
- Mathematical Modeling
- Public Health
Background:
- Global measles re-emergence is driven by susceptible populations and immunity gaps, complicating elimination efforts.
- Routine vaccination and supplementary immunization activities (SIAs) have improved measles control, yet their long-term impact is unclear due to waning vaccine-induced immunity.
Purpose of the Study:
- To investigate the short-term and long-term effects of three SIAs conducted between 2009-2012 on measles disease burden.
- To determine if additional SIAs could expedite measles elimination.
Main Methods:
- Developed a comprehensive measles transmission dynamics model incorporating demographics, contact patterns, seasonality, routine vaccination, SIAs, and waning immunity.
- Calibrated and validated the model using monthly age-specific case data (2005-2018) and sero-prevalence data from Jiangsu Province, China.
Main Results:
- Three SIAs averted 45.0% of measles cases in the short term (2009-2012) and 34.3% in the long term (until 2018).
- While SIAs reduced susceptibility in children, immunity waned in adults, increasing susceptibility in older age groups by 2018.
- Measles elimination is projected for 2028 under current interventions; additional SIAs could accelerate this by one year.
Conclusions:
- SIAs effectively reduce measles incidence and susceptibility, but waning immunity limits their long-term impact.
- Current interventions in Jiangsu Province are projected to achieve measles elimination by 2028.
- Implementing additional SIAs could potentially accelerate the timeline for measles elimination by one year.
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