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Pertussis Outbreak Investigation in a Korean Middle School: Insights on Tdap and Td Vaccination
Seonyu Park1,2, Kyujin Chang3, Soon Young Lee4
1Infectious Disease Response Team, Hwaseong-si Eastern Health Center, Hwaseong, Korea.
Insights
Pertussis cases are rising in Korea, even among vaccinated individuals. The study suggests the Tdap booster may be crucial for preventing pertussis (whooping cough) infection in adolescents.
Area of Science:
- Epidemiology
- Immunology
- Public Health
Background:
- Pertussis, or whooping cough, was historically underreported in Korea due to widespread vaccination.
- A recent surge in pertussis cases, particularly in 2024, prompted an investigation into potential causes.
- The study focuses on the role of the adolescent Tdap booster vaccination in pertussis resurgence.
Purpose of the Study:
- To investigate a pertussis outbreak in a Korean middle school.
- To explore factors contributing to the recent rise in pertussis cases.
- To assess the impact of the final Tdap booster dose on pertussis susceptibility.
Main Methods:
- Descriptive investigation of 22 confirmed pertussis cases.
- A case-control study involving 22 cases and 44 controls.
- Collection of vaccination history and epidemiological data through field investigation.
Main Results:
- Human-to-human transmission was identified as the primary mode of spread.
- A significant proportion of cases (36.4%) had completed all vaccinations, including the Tdap booster.
- Individuals who received the Tdap booster showed a shorter interval to symptom onset compared to controls, suggesting waning immunity or increased susceptibility.
Conclusions:
- The Tdap booster may play a critical role in preventing pertussis infection.
- Standardizing the final adolescent booster to Tdap in Korea's National Immunization Program is recommended.
- Addressing inconsistencies in vaccination guidelines is crucial for controlling pertussis outbreaks.
Background:
Pertussis was considered a neglected respiratory infection for decades in Korea due to the national immunization program, which includes six doses of vaccination. The final dose is administered between 11 and 12 years of age. In recent years, the number of reported pertussis cases has risen, with a rapid surge observed in 2024. This study investigates a pertussis outbreak in a middle school and explores potential reasons for the resurgence, particularly in relation to completion of the final Tdap booster dose.
Methods:
All 22 confirmed cases were investigated descriptively, and a case-control study was conducted involving 22 cases and 44 controls. Participant information, including vaccination history, was obtained through a field epidemiological investigation.
Results:
The epidemic curve of the 22 cases indicated a human-to-human transmission, with 16 transmission routes identified through the investigation. The average time from symptom onset to diagnosis was 8 days (3 to 30 days). Eight cases (36.4%) had completed all six doses of vaccination, including the final Tdap booster. In the control group, 28 out of 44 individuals (63.6%) had received the Tdap booster. A marginal statistical difference was observed between the groups (P = 0.065). Among the eight cases, the mean interval between Tdap vaccination and symptom onset was 23.1 ± 11.1 months, compared to 13.3 ± 9.0 months until the end of the outbreak for the 28 controls (P = 0.014).
Conclusion:
These findings suggest that individuals who did not receive the Tdap booster may be more susceptible to pertussis infection. It is necessary to consider standardizing the final adolescent booster as Tdap within Korea's National Immunization Program. Health authorities should use nationwide data to address the implications of permitting both Tdap and Td as the final booster dose and resolve the inconsistencies in current guidelines. While this manuscript was under review, the guideline was updated in March 2025 to recommend Tdap, not Td, as the booster at 11-12 years of age.
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