“Pneumococcal serotype replacement is evident…adult vaccination strategy is shifting”

Despite pediatric vaccination rate remaining at approximately 97%, adult disease burden continues

PCV21 is recommended…a new option has been added for high-risk patients aged 65 and older

As pediatric pneumococcal vaccination expands, shifts in the serotypes causing pneumococcal disease in adults are prompting changes in adult immunization strategies.

This shift is driven by "serotype replacement," in which the disease burden attributable to serotypes covered by existing vaccines decreases. In contrast, non-vaccine serotypes account for an increasing proportion of infections. South Korea'supdated adult pneumococcal vaccination guidelines this year newly incorporated a 21-valent pneumococcal conjugate vaccine (PCV21), developed specifically to address serotypes predominantly identified in adults.

On the 11th, MSD Korea held a media seminar at The Plaza Hotel in Jung-gu, Seoul, to commemorate the first anniversary of Capvaxive’s approval. Capvaxive received marketing authorization in South Korea in August last year and launched commercially in March this year. The vaccine is indicated for the prevention of invasive pneumococcal disease (IPD) and pneumonia caused by Streptococcus pneumoniae serotypes included in the vaccine in adults aged 18 and older.

According to MSD Korea, South Korea’s pediatric pneumococcal vaccination rate remained high at approximately 97% last year.

The expansion of pediatric immunization has significantly reduced pediatric IPD caused by vaccine serotypes and, through herd immunity, has also reduced disease incidence caused by those same serotypes in adults.

However, more than 100 Streptococcus pneumoniae serotypes exist. As specific strains decline, serotype replacement, wherein the proportion of serotypes not covered by conventional vaccines increases relatively, has emerged as a key variable in adult immunization.

Shifts in adult pneumococcal serotypes...Disease burden concentrated in older adults

Professor Young Keun Kim of the Division of Infectious Diseases at Wonju Severance Christian Hospital 

Domestic clinical studies also confirm shifts in the distribution of serotypes causing active clinical disease in adults.

A prospective surveillance study analyzing pneumococcal isolates from IPD patients across 16 university hospitals nationwide from 2017 to 2019 revealed that serotype 3 accounted for the highest proportion in adults aged 19 and older at 13.5%.

This was followed by serotype 34 at 8.1%, serotypes 10A and 19A at 6.7% each, and serotype 23A at 6.5%. These include serotypes 3, 10A, 19A, and 23A, which are included in MSD Korea's PCV21, Capvaxive. In total, Capvaxive covered 74.4% of the causative serotypes identified among the adult IPD isolates analyzed.

The disease burden is notably concentrated among older demographics. Of the 440 IPD cases notified domestically in 2025, approximately 77% occurred in individuals aged 50 and older.

Adults with underlying risk factors such as chronic cardiovascular disease, chronic pulmonary disease, diabetes, and immunocompromising conditions are also known to face a significantly higher risk of developing pneumococcal disease compared to healthy peers of the same age.

Professor Young Keun Kim of the Division of Infectious Diseases at Wonju Severance Christian Hospital stated,"Following the expansion of pediatric immunization, the serotype distribution observed in adult pneumococcal disease has continued to evolve," adding, "Rather than simply comparing the raw number of serotypes contained in a vaccine, adult vaccination strategies must consider the serotypes that actually cause clinical disease domestically, alongside patient age, underlying comorbidities, and prior vaccination history."

KSID newly includes PCV21...Expanding immunization options

These changing epidemiological patterns have now been integrated into domestic immunization recommendations.

The Korean Society of Infectious Diseases (KSID) has added PCV21 to its 2026 adult pneumococcal vaccination guidelines.

According to the guidelines, all adults aged 65 and older, as well as high-risk individuals aged 19 to 64 with immunocompromising conditions or chronic illnesses, may receive either a single dose of PCV21 or PCV20, or sequential vaccination with PCV15 followed by the 23-valent pneumococcal polysaccharide vaccine (PPSV23), depending on their prior pneumococcal vaccination history.

Health authorities in other major international markets have similarly advanced the adoption of PCV21. The U.S. Advisory Committee on Immunization Practices (ACIP) recommends PCV21 as a vaccination option for adults aged 50 and older who have no prior PCV history and for adults aged 19 to 49 with specific risk factors. Countries such as France, Australia, Canada, and Austria have likewise included PCV21 in their recommendations for elderly and high-risk populations.

The PCV21 vaccine formulation includes 21 discrete serotypes; when accounting for serotype 15C, which demonstrates cross-immunogenicity with 15B, it targets a total of 22 serotypes under its domestic regulatory label. This includes eight unique serotypes not covered by existing pneumococcal conjugate vaccines: 15A, 15C, 16F, 23A, 23B, 24F, 31, and 35B.

Immunogenicity evaluated across vaccine-Naïve, previously vaccinated, and high-risk patients

Through the STRIDE clinical trials, immunogenicity and safety profiles of Capvaxive were evaluated across pneumococcal vaccine-naïve individuals, previously vaccinated recipients, and adults presenting with chronic underlying medical conditions.

The Phase 3 STRIDE-3 study included 2,656 vaccine-naïve adults aged 18 and older. Capvaxive met non-inferiority criteria across all 10 serotypes shared with the active comparator vaccine, while demonstrating statistically superior immune responses across 10 of the 11 serotypes unique to Capvaxive.

In the STRIDE-6 study, which evaluated 717 adults aged 50 and older with documented prior pneumococcal immunization, robust immune responses were confirmed across all 21 vaccine serotypes at 30 days post-vaccination.

Professor Kim commented, "Capvaxive has demonstrated superior immunogenicity across key serotypes in clinical trials. It is recognized as a vaccine that can be preferentially recommended in adult clinical practice."

The STRIDE-8 trial, which included 518 adults aged 18 to 64 with chronic comorbidities such as diabetes or chronic cardiac, renal, hepatic, or pulmonary disease, similarly confirmed immune responses across all 21 serotypes.

In STRIDE-5, which evaluated the possibility of concomitant administration with seasonal influenza vaccines in adults aged 50 and older, non-inferiority criteria compared to sequential dosing were met for 20 of Capvaxive's 21 serotypes and three of the four seasonal influenza vaccine strains.

Ultimately, the paradigm for adult pneumococcal vaccination is shifting away from a sheer count of vaccine valencies toward a clinically targeted approach that weighs real-world serotype prevalence in adult disease, patient age, baseline comorbidities, and prior immunization exposure.

Cho Jae-yong, Managing Director of the Vaccines Business Unit at MSD Korea, stated, "The first anniversary of Capvaxive's domestic approval represents a moment to reflect on the significance of introducing an immunization option tailored to the serotypes driving adult disease burden. Based on Korean epidemiology and clinical evidence, MSD Korea will remain committed to delivering scientific data and enhancing awareness of pneumococcal disease to empower clinicians in selecting vaccination strategies tailored to individual patient profiles."