Pertussis resurgence and epidemiology of fully vaccinated cases in eastern China: evidence for vaccination timing.

OBJECTIVES

This study aimed to comprehensively analyze the epidemiology of pertussis based on case characteristics and vaccination history in Zhejiang Province.

METHODS

We analyzed clinically diagnosed and laboratory-confirmed pertussis cases (aged 0-18 years old) reported in Zhejiang Province from January 2016 to December 2024. Vaccination history data were matched from the Zhejiang Provincial Immunization Information System.

RESULTS

A total of 63,664 pertussis cases were identified in Zhejiang Province, China. The annual incidence of pertussis among individuals aged 0-18 years increased gradually from 2016 (1.46/100,000) to 2023 (14.22/100,000), followed by a drastic surge to 512.56/100,000 in 2024. During the resurgence, incidence rose most substantially in kindergarten (3-6 years) and lower elementary (7-9 years) children, surpassing the incidence of infants in 2024. Among 55,968 identified pertussis cases with data on vaccination status, the proportion of fully vaccinated cases increased from 12.50% in 2016 to 79.24% in 2024. Among 43,004 fully vaccinated cases, kindergarten children accounted for the highest proportion (51.27%), followed by the lower elementary children (34.58%). Regarding infection timing, 68.4% of fully vaccinated cases occurred after 6 years old, whereas 31.6% occurred before 6. The median interval between last vaccine dose and disease onset was 61.45 months (interquartile range: 48.15-79.47 months).

CONCLUSION

Our findings underscore the critical need for booster vaccination at 4-6 years, and highlight the necessity for future research to focus on vaccine safety, effectiveness, and cost-effectiveness in optimizing vaccination strategies.