Modeling time-varying efficacy of RTS,S/AS01 malaria vaccine across trial settings.

Area of Science:

• Immunology
• Vaccinology
• Biostatistics

Background:

• Evaluating long-term vaccine protection is essential for public health.
• The RTS,S/AS01 malaria vaccine's efficacy over time requires accurate modeling.
• Vaccination strategies depend on understanding waning vaccine immunity.

Purpose of the Study:

• To assess how different modeling approaches impact the interpretation of time-varying vaccine efficacy (VE).
• To compare commonly used VE modeling functions with semi-parametric benchmarks.
• To identify a suitable model for characterizing waning VE in the RTS,S/AS01 malaria vaccine trial.

Main Methods:

• Utilized 18-month pre-booster data from a multi-center RTS,S/AS01 malaria vaccine trial.
• Evaluated four linear-in-parameter functions and a four-parameter monotonic function for VE modeling.
• Compared parametric models against semi-parametric spline benchmarks.

Main Results:

• The four-parameter function was preferred when sufficient clinical malaria episodes were available.
• Different VE modeling specifications yielded significantly different estimates of vaccine impact.
• The four-parameter model revealed an inverse-sigmoid pattern of RTS,S/AS01 protection, stabilizing between 20-40% after an initial decline.

Conclusions:

• Modeling choices critically influence the interpretation of vaccine protection over time.
• The four-parameter approach offers a parsimonious and interpretable method for characterizing waning VE.
• This modeling approach has potential applicability to other vaccine platforms.