[Health Tip] Whooping Cough on the Rise... Don't Forget Children's 'Booster' Vaccinations

Recently, the incidence of pertussis, a respiratory infectious disease, has been increasing mainly among children under 12 years old, raising the need for additional vaccinations to prevent pertussis.

A child is receiving a vaccination at a pediatric clinic in Seoul. Photo by Mun Ho-nam munonam@

According to the Korea Disease Control and Prevention Agency on the 3rd, as of the 44th week of this year, there were 83 pertussis patients, which is 3.3 times higher than the 25 patients during the same period last year. In particular, 56 of them (67.5%) were children under 12 years old, accounting for the largest proportion.

Pertussis is a second-class legally designated respiratory infectious disease caused by the Bordetella bacteria and is considered one of the highly contagious respiratory diseases among pediatric infectious diseases. In the early stages of infection, symptoms similar to a cold such as runny nose, sneezing, mild fever, and cough appear, which can progress to severe coughing. At this stage, symptoms such as paroxysmal cough, post-cough vomiting, and apnea may occur. Since pertussis spreads through droplets expelled when a patient coughs or sneezes, vaccination is very important for prevention, especially in age groups involved in group living.

The government currently provides pertussis vaccination through the National Immunization Program (NIP). The NIP uses the DTaP vaccine, which prevents diphtheria (D), tetanus (T), and acellular pertussis (aP). Additionally, vaccinations can be administered using the DTaP-IPV quadrivalent vaccine, which includes inactivated poliovirus (IPV), or the DTaP-IPV/Hib pentavalent vaccine, which also includes Haemophilus influenzae type b.

Professor Choi Young-jun of the Department of Pediatrics at Korea University Anam Hospital stated, "The basic DTaP vaccination rate in Korea is high globally," but emphasized, "However, the vaccine's effectiveness may gradually decrease after the age of 2, and additional vaccinations are essential when children enter group settings such as daycare centers or kindergartens."

The pertussis vaccine is administered three times as a primary series at 2, 4, and 6 months of age, followed by three additional doses at 15-18 months (4th dose), 4-6 years (5th dose), and 11-12 years (6th dose). Because of this, the vaccination rate remains above 95% until the first additional dose (4th), but drops to 94.1% at the 5th dose and sharply declines to 85.8% at the 6th dose. This decline occurs during a period when children are particularly vulnerable to infection and pose a high risk of transmission.

[Image source=Yonhap News]

Especially, the immunity from vaccines administered during infancy gradually wanes with age, so even if the primary vaccination series is completed, periodic additional vaccinations are necessary to maintain antibody protection.

If the basic vaccination includes the DTaP vaccine, additional doses can be given with DTaP-IPV or DTaP-IPV/Hib vaccines. However, different vaccines are used depending on the timing. The 4th additional dose uses the DTaP vaccine, the 5th dose can use either DTaP or the DTaP-IPV quadrivalent vaccine, and the final 6th dose can be administered with the Tdap vaccine, which contains tetanus, diphtheria, and acellular pertussis antigens. The difference in uppercase and lowercase letters in DTaP and Tdap vaccine notations reflects the different antigen quantities. It is best to use the recommended vaccine for each stage, as the required antigen amounts vary accordingly.

It is important to complete vaccinations on schedule and finish all recommended additional doses for full immunization. However, since vaccination omissions are more likely during frequent infant vaccinations or when additional doses are needed, if vaccination is delayed or missed due to unavoidable circumstances, it is necessary to follow the recommended 'catch-up vaccination' schedule to receive the appropriate vaccines.

Mixed vaccines containing pertussis antigens, such as the DTaP vaccine, reduce the number of injections and simplify the vaccination schedule, improving convenience and helping prevent missed vaccinations. In Germany, higher-valency mixed vaccines have been associated with higher on-time and complete vaccination rates.

Among vaccines currently introduced in Korea, Sanofi's 'Hexaxim Prefilled Syringe,' a 6-valent mixed vaccine that includes DTaP-IPV/Hib plus hepatitis B (HepB) prevention, is the highest-valency mixed vaccine. However, the NIP currently supports only up to the 5-valent vaccine, so the 6-valent vaccine must be administered separately as a paid vaccination.

In May, a research team led by Professor Lee Ui-kyung of Sungkyunkwan University College of Pharmacy published an analysis in the international journal 'MDPI Vaccines,' stating that introducing the 6-valent mixed vaccine into the NIP, compared to separately administering the 5-valent mixed vaccine and hepatitis B vaccine, could save 47,155 KRW per infant and reduce socioeconomic costs by approximately 12 billion KRW nationwide as of 2021.

Professor Choi Young-jun of Korea University Anam Hospital's Department of Pediatrics said, "The most effective way to protect children from infectious diseases is vaccination," and added, "Active interest and guidance from guardians are necessary to ensure children receive timely vaccinations and achieve optimal immune protection." He also emphasized, "To enhance immunity through vaccination, it is important to use mixed vaccines and vaccinate on schedule, and if the vaccination timing is missed, immediate catch-up vaccination should be performed to build immunity."