Vaxcyte (PCVX) Study Result summary

Study design and methodology

• Randomized, observer-blind, active-controlled phase II study evaluated VAX-24 at three dose levels (1.1mcg, 2.2mcg, 4.4mcg/mixed) versus PCV20 and PCV15 in 802 healthy infants, with dose escalation and main study phases.

• Subjects received doses at 2, 4, 6 months and a booster at 12–15 months; safety and immunogenicity were assessed post-dose three and four.

• Demographics were well balanced across cohorts, with similar age, sex, and racial distribution; 26% were not included in post-dose three immunogenicity due to sample issues.

• Stage 1 compared VAX-24 to PCV15 in 48 infants; Stage 2 compared VAX-24 to PCV20 in 789 infants.

• Dose levels mirrored those used in adult studies, with strategic mixed dosing to simulate VAX-31 and assess carrier suppression.

Safety and tolerability results

• VAX-24 was well tolerated at all doses, with a safety and tolerability profile similar to PCV20; no serious vaccine-related adverse events reported.

• Local and systemic reactions were mostly mild to moderate, resolving within days, with no dose-dependent increase; severe events were rare and comparable to PCV20.

• Rates of unsolicited adverse events, medically attended events, and serious adverse events were similar between VAX-24 and PCV20.

• No related deaths or vaccine-related serious adverse events were reported; one unrelated death (SIDS) occurred in the PCV20 group.

Immunogenicity and efficacy findings

• VAX-24 elicited substantial IgG, OPA, and memory responses, with high seroconversion rates (>90%) for most serotypes at all doses; serotype 3 showed 70–88% vs <40% for PCV20.

• For the seven most common serotypes in US children, the lowest seroconversion was 93.1%.

• The mid dose (2.2mcg) met non-inferiority criteria for 20 of 24 serotypes post-dose 3, and IgG geometric mean ratios met targets for 22 of 24 serotypes at mid and mixed doses.

• Four serotypes unique to VAX-24 met all immunogenicity targets across all doses.

• Dose-dependent immune responses observed, with little to no evidence of carrier suppression.