A decade of progress: pneumococcal vaccination vital in protecting Korean children

The Covid-19 pandemic has highlighted the importance of vaccination worldwide. In particular, there has been a renewed emphasis on pneumococcal vaccination, which can cause severe illnesses, including pneumonia and acute otitis media, and can be fatal for immunocompromised children.

This year marks the 10th anniversary of introducing the 13-valent pneumococcal conjugate vaccine (PCV13)—Prevenar of Pfizer—as part of the nationally indispensable program (NIP) for infants and children. The addition of a 15-valent pneumococcal conjugate vaccine (PCV15)—Vaxneuvance of MSD—in April has expanded the options available.

In addition, the introduction of a PCV20 with a wider range of protection is expected in Korea shortly. Against this backdrop, Korea Biomedical Review met with Professor Choe Young-june of the Department of Pediatrics at Korea University Anam Hospital, to discuss the importance of vaccination to prevent pneumococcal infections in children and what should be considered when vaccinating children.

Question: In Korea, efforts are being made to prevent diseases caused by pneumococci by implementing NIP for children. Why is it necessary to prevent pneumococcal infections in children?

Answer: Pneumococci enter the body shortly after birth and colonize the nasopharynx. Not all pneumococci cause disease, but they are common enough to be found in 60-70 percent of infants and toddlers attending daycare centers. Pneumococcal infections can lead to severe illnesses, especially in babies as young as two to three months old with weak immune systems.

Before Korea introduced the vaccine, pneumococcus was the most common cause of invasive bacterial infections in children. Since its introduction, the number of invasive bacterial infections caused by pneumococci has decreased significantly, but the proportion is still high compared to other bacteria.

Q: There are more than 90 known serotypes of pneumococci. Which of these serotypes are prevalent in Korea, and how have they changed over time?

A: Serotypes that cause frequent or severe disease in adults and children are different. Serotype 3 is the most problematic in adults, and serotype 19A is the most problematic in children. Serotype 19A infection rates have decreased significantly since the introduction of PCV13, but it is still the most frequent serotype among vaccine-preventable serotypes.

Q: It has been 10 years since the introduction of Synflorix (PCV10) of GSK and Prevenar as NIPs in 2014. What changes have occurred in vaccination coverage and vaccine-induced disease rates before and after the introduction of NIPs?

A: Comparing when PCV7 was introduced with today, there has been a significant decrease in invasive infections caused by pneumococci. Before the vaccine's introduction, pneumococcus was always the number one cause of invasive infections, but there are now other infections that cannot be vaccinated against.

In addition, among the different serotypes of pneumococci, the vaccine-preventable serotypes have decreased, and the proportion of non-vaccine serotypes has increased. This is called serotype substitution, and it is influenced not only by vaccines but also by antibiotics.

Q: Besides the importance of vaccines, concerns about side effects have increased since Covid-19. What are the trends in adverse event rates for pneumococcal conjugate vaccines in the 10 years since the introduction of NIPs?

A: The vaccine's safety is assessed by separating mild and severe adverse events, and no serious adverse events are of concern. The most common adverse event in clinical practice is fever, which is often transient and mild and does not result in vaccine discontinuation. This safety profile has remained consistent over the 10 years since the introduction of NIP.

Q: In April, 15-valent new vaccines were added to the NIP. What are the endpoints you use to select vaccines?

A: The World Health Organization recommends vaccinating against the serotypes most frequently found in the country and causing the most invasive infections. In Korea, it is most important to prevent 19A, which is included in both PCV13 and PCV15.

I understand that the Korean Pediatric Society is making guidelines for pneumococcal vaccination. As PCV13 and PCV15 can be cross-immunized, no preferred vaccine is expected. Instead, proper vaccines will be selected by consultation between healthcare providers and caregivers based on the fields’ local circumstances.

Previously, vaccines with high serotype coverage were considered good simply because of the range of serotypes they covered. This makes sense, given that infections from non-vaccinated serotypes are rising. When it comes to vaccinating children with underlying medical conditions, medical professionals’ judgment is paramount.

Q: PCV15 has added serotypes 22F and 33F, known to circulate in North America. Are these serotypes likely to become prevalent in Korea?

A: Pneumococcal serotypes do not mix well, even though people move around the world more frequently. Even if a serotype is indigenous to a country and transmitted through human movement, it does not mean it will be the predominant serotype in that country. This is why there is an emphasis on localized serotype-specific prevention.

Q: Currently, the pneumococcal vaccine with the broadest coverage is PCV20. It is not yet available in Korea but has been introduced in major countries, including the United States. We wonder what clinical benefits Koreans can expect when it is introduced.

A: According to a study on pneumococcal serotyping in Korean children and adults published by the Korea Disease Control and Prevention Agency (KDCA) in 2021, non-vaccine serotypes accounted for 89.5 percent of all invasive pneumococcal infections among recognized invasive infections caused by pneumococci from January 2018 to December 2020, with 10A being the most common serotype. PCV20 contains 10A, which is expected to have additional clinical benefits in Korea.

In particular, invasive infections in adults have a wider serotype distribution than in children. Therefore, polysaccharide vaccines that protect 23 serotypes are included in the national immunization program, but polysaccharide vaccines tend to be less effective in preventing pneumonia and severe invasive infectious diseases. Therefore, the introduction of pneumococcal conjugate vaccines that are used in children is being discussed in adults, and PCV20 is significant because it is a vaccine that can completely replace the current polysaccharide vaccine.

Q: Since Covid-19, respiratory diseases caused by bacteria and viruses have received increased attention. What can people do to minimize the impact of infectious respiratory illnesses?

A: Some people are reluctant to get vaccinated because of concerns about fever or injection reactions, but vaccines can help prevent high-burden infectious diseases early and prevent them from becoming severe. Given the suffering of patients in severe cases, vaccination is critical. Pharmaceutical companies, academic societies, and governments are working to prevent social infectious diseases through vaccines, so please pay attention to vaccination.