Transmission dynamics and risk factors for pertussis during the 2023-2024 outbreak in Korea.

Despite widespread vaccination, pertussis continues to cause significant outbreaks. We investigated transmission dynamics and risk factors associated with pertussis transmission during the 2023 outbreak in South Korea. Among 103 laboratory confirmed cases with complete contact tracing data, 84 (81.6 %) transmitted infection to at least one contacts. The median number of secondary cases was 13.0 (IQR: 2-23), with a median secondary attack rate of 26.9 %. Multivariable analysis identified time since last vaccination (OR: 1.04, 95 % CI: 1.00-1.08, p = 0.043) and duration of symptoms before diagnosis (OR: 1.85, 95 % CI: 1.13-3.04, p = 0.015) as independent predictors of transmission. The optimal time since vaccination cutoff was 27 months (sensitivity 91.8 %, specificity 57.9 %). The area under the receiver operation characteristic curve was 0.715 (95 % CI 0.617-0.799) for the time since last vaccination. This study demonstrates the high transmissibility of pertussis and underscore the importance of early diagnosis and timely vaccination boosters to effectively control pertussis outbreaks.