Peer-reviewed article
Timeliness and dose-dependent protection of pertussis vaccination in children under 5 years: Evidence from a population-based cohort in Zhejiang Province, China.
Yao Zhu, Yang Zhou, Xiaohua Qi, Peihan Chi, Kai Gao et al. ·
Summary
Written by AI, not yet AICS's view · claude-haiku-4-5-20251001This study examined pertussis vaccination protection in nearly 2.8 million children in Zhejiang Province, China, using linked vaccination and disease surveillance records from 2015 to 2023. The research found that pertussis incidence was highest in unvaccinated infants aged 3.5 to 4.5 months, and decreased with each additional vaccine dose. However, protection waned significantly 3-4 years after the fourth dose, leading to increased cases in preschool-age children. The findings identify two vulnerable periods: early infancy before vaccination is complete, and preschool years when immunity declines.
Key points
- Overall pertussis incidence was 18.71 per 100,000 person-years in children under 5 years
- Peak incidence of 132.87 per 100,000 person-years occurred in unvaccinated infants aged 3.5-4.5 months
- Incidence declined with each dose: at ages 5.5-6.5 months, rates fell from 76.05 (one dose) to 36.87 (two doses) to 11.97 (three doses) per 100,000 person-years
- Protection significantly waned 3-4 years after the fourth dose, with a 5.56-fold increased risk compared to less than 1 year after the fourth dose
- Resurgence of incidence occurred at 36-60 months of age (15.16 per 100,000 person-years), supporting addition of a booster dose at age six
Limitations
This is an observational cohort study using administrative health records, so causality cannot be definitively established and unmeasured confounders may influence results. The study is specific to one Chinese province and may not generalize to other settings with different vaccination schedules or disease epidemiology.
Abstract
BACKGROUND: Despite high vaccination coverage, pertussis remains a public health concern in China and worldwide, with limited data on incidence stratified by both age and vaccine dose number. METHODS: This retrospective cohort study analyzed 2,842,942 children born in Zhejiang between 2015 and 2022, using linked records from the Zhejiang Provincial Immunization Information System and the National Notifiable Disease Surveillance System. Children were followed until pertussis diagnosis, age five, or December 31, 2023. Age-dose-specific and age-vaccination status-specific incidence rates (per 100,000 person-years) were calculated across ten age intervals (0 to <1.5, 1.5 to <2.5, 2.5 to <3.5, 3.5 to <4.5, 4.5 to <5.5, 5.5 to <6.5, 6.5 to <12.5, 12.5 to <19.5, 19.5 to <36, and 36 to <60 months). Poisson regression assessed the pertussis risk by time since fourth dose. RESULTS: The overall incidence rate was 18.71 per 100,000 person-years under the age of 5 years. Peak incidence (132.87/100,000 person-years) was observed in unvaccinated infants aged 3.5 to <4.5 months. Incidence declined with each additional dose; among children aged 5.5 to <6.5 months, rates decreased from 76.05 (one dose) to 36.87 (two doses) and 11.97 (three doses) per 100,000 person-years. The lowest incidence (5.87/100,000 person-years) was observed in children aged 19.5 to <36 months who received four doses. However, protection waned significantly 3-4 years after the fourth dose (IRR=5.56, 95% CI: 4.33-7.14 vs <1 year), coinciding with a resurgence of incidence at 36 to <60 months of age (15.16 per 100,000 person-years). CONCLUSION: The findings highlight two vulnerability periods: early infancy (particularly up to 4.5 months of age) before vaccination schedule completion, and preschool years due to waning immunity. These observations support China's 2025 pertussis schedule update, introducing a booster at age six and advancing the initial dose.
Findings the Hub has extracted
Each claim below is labelled by its type of design and links back to this report.
- Intervention
- Pertussis vaccination following the routine immunization schedule with doses at specified ages
- Population
- 2,842,942 children born in Zhejiang Province, China between 2015 and 2022, followed until age 5 or pertussis diagnosis
Key finding
Unvaccinated infants aged 3.5-4.5 months had peak incidence of 132.87 per 100,000 person-years
Zhu et al. · PubMed (US National Library of Medicine) · 12 May 2026