Analysis of epidemiological characteristics and vaccine effectiveness of pertussis in Linping District, China

Background The increases in pertussis outbreaks among both vaccinated and unvaccinated individuals raises questions about the effectiveness of the pertussis vaccine (PV), highlighting the need for research on the impact of PV immunization on the incidence of pertussis in children. Methods Descriptive epidemiological methods were used to analyze pertussis cases reported in Linping District from 2022 to 2023. A nested case-control study was conducted (1:4 matching). Conditional logistic regression was employed to calculate odds ratios (ORs) and vaccine effectiveness (VE) of PV. Results A total of 149 cases of pertussis cases were reported in Linping District from 2022 to 2023, with an overall incidence rate of 6.20 per 100,000 population. The epidemic showed a unimodal pattern, peaking from April to June 2022. The majority of cases (99.33%) were children under 18 years old, with the highest proportion in the 0-year-old group (23.49%). Of the cases, 85.23% had a history of PV vaccination, and 73.15% had completed four doses. The case-control study revealed that the VE for any PV history versus no history was 92.86% ( 95% CI : 65.62% ~ 98.52%). The VE for 1 ~ 3 doses of basic immunization was 93.84% ( 95% CI : 68.10% ~ 98.81%). The VE for immunization within less than 1 year was 94.61% ( 95% CI : 71.08% ~ 99.00%). The VE for DTwP, DTaP, and DTaP-IPV/Hib vaccination was 92.68% ( 95% CI : 60.30% ~ 98.65%), 91.69% ( 95% CI : 59.13% ~ 98.31%), and 94.14% ( 95% CI : 70.45% ~ 98.84%), respectively. Conclusion Pertussis primarily affected children in Linping District, showing a distinct spring peak. Delayed or missed vaccination was a key risk factor for infant cases. Under high vaccination coverage, four doses of DTaP vaccines provide good protection against pertussis at least through preschool age.