— The vaccine showed a better immune effect than 20-valent vaccine against problematic serotype 3
October 27, 2026 • 2 min read
WASHINGTON -- A pneumococcal conjugate vaccine (PCV) covering 25 serotypes was safe and generated immune responses among infants that were comparable to the current 20-valent vaccine (Prevnar 20), a phase II trial showed.
Among 401 healthy infants, immunogenicity 1 month after a fourth vaccine dose was similar between those receiving PCV25 and those receiving PCV20 across the two vaccines' 20 shared serotypes, and PCV25 also generated robust responses to five new serotypes, reported Laurence Flint, MD, MPH, of Pfizer in Pearl River, New York, at the IDWeekopens in a new tab or window annual meeting.
Local and systemic reactions were mostly mild to moderate, and adverse events were balanced between the two groups.
PCV25 provides protection against Streptococcus pneumoniae serotypes that collectively cause about 84% of invasive pneumococcal infections in U.S. children younger than 5 years, including cross protection from serotypes not directly targeted by the vaccine, Flint noted. PCV25 could offer an incremental increase of about 25% more coverage for invasive pneumococcal disease compared with PCV20.
The 25-valent vaccine also includes an enhanced serotype 3, which drives about 10% of invasive pneumococcal infections in U.S. children. With prior vaccines, the structure of serotype 3 has made them less likely to generate strong immune responses, Flint explained.
The immunoglobulin G response that PCV25 generated to pneumococcal serotype 3 rose from a geometric mean concentration (GMC) of 4 mcg/mL after dose three to 13 mcg/mL after dose four. Responses with PCV20 to serotype 3 remained steady after both doses and below a GMC of 1 mcg/mL.
Streptococcus pneumoniae bacteria can cause pneumococcal disease in children and adults, with conditions ranging from acute otitis media and sinusitis to more serious cases of pneumonia, sepsis, and bacterial meningitis.
The American Academy of Pediatrics recommendsopens in a new tab or window four doses of routine PCV20 or PCV15 for all infants and children starting at age 2 months, with additional recommendations for children up to age 18 years with incomplete vaccination or high-risk conditions. The CDC recommendsopens in a new tab or window pneumococcal vaccination for all children younger than age 5 years, as well as those ages 5 to 18 years with risk factors. In the U.S., current available pneumococcal vaccines cover 15 to 23 serotypes.
PCV25 is now being evaluated in several phase III clinical trialsopens in a new tab or window, with planned submission for FDA approval in 2029.
This phase II trialopens in a new tab or window included healthy, full-term infants randomized to receive either PCV25 or PCV20 at 2, 4, and 6 months, with a toddler dose at 12 to 15 months.
Local reaction rates were comparable between the PCV25 and PCV20 groups by the fourth dose, with similar rates of injection-site pain (42.4% vs 43.9%, respectively), redness (35.6% vs 32.2%), and swelling (25.4% vs 21.7%). Systemic event rates were also similar among the PCV25 and PCV20 groups by the fourth dose, including fever (18.6% vs 17.9%), decreased appetite (26.0% vs 30.6%), drowsiness or increased sleep (46.9% vs 39.4%), and irritability (59.3% vs 58.3%). There were no grade 4 local or systemic reactions.
The percentages of infants who reached the 0.35 mcg/mL threshold used to predict protection for 17 of 20 serotypes were comparable between the PCV25 and PCV20 groups. More infants who received PCV25 reached that threshold for serotype 3.