Pfizer Launches New Phase III Clinical Trial of RSVpreF Vaccine in High-Risk Pediatric Population

On June 12, Pfizer registered a clinical trial (PICASSO) on clinicaltrials.gov to evaluate the safety and immunogenicity of the RSVpreF vaccine (PF-06928316) in children aged over 2 and under 18 who are at high risk for respiratory syncytial virus (RSV).

The study plans to enroll 1,980 participants, including three phases: I, II, and III. Among these, Phase I is an open-label dose-finding study, expecting to recruit approximately 60 to 120 participants. Initially, the safety of a single 120µg dose of RSVpreF will be assessed in 40 participants aged over 5 and under 18. After safety evaluation and regulatory approval, this part of the trial will continue assessing the safety of a 60µg dose of RSVpreF in 20 participants aged over 2 and under 5. If the 60µg dose is confirmed to be safe, the study will proceed to evaluate the safety of a 120µg dose of RSVpreF in another 20 participants aged over 2 and under 5.

The Phase II/III stage is a double-blind study that will evaluate the safety and immunogenicity of two investigational doses from Phase I. Subjects in each age group will be randomly vaccinated with RSVpreF or placebo in a 2:1 ratio. If both age groups chooseSameThe dose level, thenTotalA total of 930 subjects will be recruited, of which at least 75 subjects in the older age group should have chronic diseases. If both age groups are selected,DifferentThe dose level, thenEachThe age group will recruit 930 subjects.

The primary endpoints of the Phase II/III study include safety and primary immunogenicity. Safety indicators consist of local reactions, systemic reactions, adverse events, the proportion of patients with newly diagnosed chronic diseases, and serious adverse events; the efficacy indicator is the titer of RSV-specific serum neutralizing antibodies (GMT).

Currently, the preventive effect of this vaccine has been verified in the elderly and newborn populations. The Phase III RENOIR trial for the prevention of RSV infection in people aged 60 and above showed that the vaccine provided a protection rate of 66.7% against two or more lower respiratory tract symptoms, 85.7% against at least three or more lower respiratory tract symptoms, and 62.1% against acute respiratory disease. The FDA approved the vaccine for marketing on May 31, 2023 (see: ).

The Phase III MATISSE study, which investigates active immunization in pregnant women to help prevent RSV-related lower respiratory tract disease in infants from birth to 6 months, showed that the vaccine’s efficacy against severe RSV-induced lower respiratory tract disease was 81.8% during the first 90 days after birth and 69.4% during the six-month follow-up period. In August this year, the vaccine is expected to receive FDA approval for an expanded eligible population (see: ).

In addition, on May 8, Pfizer initiated a Phase III clinical study of RSVpreF in adults at high risk for RSV. This study aims to evaluate the safety, tolerability, and immunogenicity of the vaccine in helping to prevent RSV infection in this high-risk adult population. The study is expected to be completed by March 22, 2024.

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