ACIP Highlights Evidence Supporting Recommendation for PCV21 Vaccine for Adults

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In a new report published in Morbidity and Mortality Weekly Report, researchers summarize the evidence considered in the recent recommendations from the CDC’s Advisory Committee on Immunization Practices (ACIP) on the use of 21-valent pneumococcal conjugate vaccine (PCV21) in adults.

On June 27, 2024, the ACIP unanimously voted to recommend a single dose of the recently approved PCV21, Capvaxive (Merck), for adults aged 19 years and older who are currently recommended to received either 15- or 20-valent pneumococcal conjugate vaccine.

The FDA approved Capvaxive on June 17, 2024, for use in adults aged 50 years and older. It contains 8 unique serotypes not covered by other currently approved pneumococcal vaccines. These 8 serotypes were responsible for 20%-30% of invasive pneumococcal disease (IPD) cases among adults between 2018 and 2022, according to investigators.

“Adding PCV21 as an option in the current PCV recommendation is expected to prevent additional disease caused by pneumococcal serotypes unique to PCV21,” first author Miwako Kobayashi, MD, of the Division of Bacterial Diseases in the CDC’s National Center for Immunization and Respiratory Diseases, and colleagues wrote. “Postlicensure monitoring of safety and public health impact of PCV use will guide future recommendations.”

In the report, Kobayashi and colleagues pooled safety data from 4 phase 3 clinical trials that included pneumococcal vaccine–naïve adults aged 18-49 years, pneumococcal vaccine–naïve adults aged 50 years and older, and pneumococcal vaccine–experienced adults aged 50 years and older. Safety of PCV21 among 4020 recipients of the vaccine was compared with that among 2018 participants who received a comparator vaccine (PCV15, PCV20, or 23-valent pneumococcal polysaccharide vaccine [PPSV23]). Results showed that the proportion of participants experiencing at least 1 solicited adverse event was similar between PCV21 (63.3%) and comparator vaccine recipients (63.9%).

Investigators also examined available research comparing the immunogenicity of PCV21 to that of PCV15, PCV20, and PPSV23. Results showed that PCV21 met noninferiority criteria
for serotypes shared with PCV20 and PPSV23 among pneumococcal vaccine–naïve adults. Furthermore, PCV21 elicited statistically significantly higher immune responses for most of the serotypes unique to the vaccine, except 15C, “although the immune response was numerically higher when compared with PCV20,” researchers noted.

One serotype not covered by PCV21 is pneumococcal serotype 4. For certain populations in which more than 30% of pneumococcal disease is caused by serotype 4, previously recommended vaccines that include it (PCV20 alone or PCV15 and PPSV23 in series) provide broader coverage against locally circulating strains than PCV21.

Reference: Kobayashi M, Leidner AJ, Gierke R, et al. Use of 21-valent pneumococcal conjugate vaccine among U.S. adults: Recommendations of the Advisory Committee on Immunization Practices — United States, 2024. MMWR. 2024;73:793-798.