Age-Specific Pertussis Transmission Dynamics and Impact of Immunization Schedule Revision in Hunan, China: Age-Structured Mathematical Modeling Study

BACKGROUND Despite extensive vaccination efforts, pertussis has experienced a global resurgence, with China alone reporting over 470,000 cases in 2024. The age distribution of cases has shifted markedly from infants to school-age children and adults, likely driven by waning acellular pertussis vaccine (DTaP [Diphtheria, Tetanus Toxoids, and Acellular Pertussis Vaccine])–induced immunity. In response, China revised its immunization schedule in 2025 to include a booster dose at the age of 6 years; however, the population-level impact of this strategy on age-specific transmission dynamics remains unclear. OBJECTIVE This study aimed to characterize the shifting age-specific transmission dynamics of Bordetella pertussis under changing immunization landscapes and evaluate the population-level impact of the 2025 Chinese immunization schedule. METHODS An age-structured Vaccinated-Susceptible-Exposed-Infectious-Recovered model incorporating vaccination, waning immunity, and demographic structures was calibrated using surveillance data from Hunan Province (2010-2025). The next-generation matrix approach estimated the effective reproduction numbers across 5 epidemic phases. Multiscenario simulations were used to assess the impact of a 6-year booster dose at varying coverage levels. RESULTS Among 47,300 reported cases (2010-2025), a marked resurgence peaked at 6743 cases in April 2024, with consistent spring seasonality. The case distribution shifted from infant-dominated (0-6 months: 293/552, 53.07%, 2010-2017) to school-age-dominated (6-10 years: 9814/30,589, 32.08%, 2024-2025). This study period was stratified into 5 temporal phases based on the epidemic dynamics: phase 1 (2010-2017), phase 2 (2018-2019), phase 3 (2020-2023), phase 4 (2024), and phase 5 (2025). Segmented fitting analyses were conducted for monthly pertussis cases across age groups within each phase of this study. The model demonstrated high fitting consistency across all age groups, with an overall R2 of 0.96. Adults emerged as the dominant transmission source in 2023-2024 (Reff to infants: 2.717). A booster administered at the age of 6 years with full coverage is expected to decrease the 10-year cumulative incidence by 24.15% (24,972.58/103,408.95). Children between 6 and 10 years of age are expected to experience the most significant monthly decrease, at 45.06% (335.49/744.51), whereas infants are predicted to gain 28.91% (170.92/591.19) indirect protection. CONCLUSIONS Pertussis resurgence is driven by age-structured heterogeneity and waning immunity. Administering a booster shot to children at the age of 6 years can reduce the spread of infections across different age groups and offer indirect protection to infants who are at high risk. However, for long-term control, it may be necessary to implement broader strategies that involve vaccinating adolescents, adults, and pregnant women. CLINICALTRIAL