A Phase IIa Controlled Human Malaria Infection and Immunogenicity Study of RTS,S/AS01E and RTS,S/AS01B Delayed...

Area of Science:

• Vaccinology
• Infectious Diseases
• Tropical Medicine

Background:

• Previous trials show 3-dose RTS,S/AS01B vaccine efficacy (VE) in adults.
• This study investigated VE of delayed fractional dose regimens for RTS,S/AS01 formulations.

Purpose of the Study:

• To compare the VE of different delayed fractional dose regimens of adult and pediatric RTS,S/AS01 formulations.
• To evaluate the efficacy of 2-dose versus 3-dose vaccination schedules.

Main Methods:

• 130 participants randomized into 5 groups.
• Four groups received 3 doses of RTS,S/AS01B or RTS,S/AS01E with fractional final doses.
• One group received 1 full and 1 fractional dose of RTS,S/AS01E.
• Controlled human malaria infection challenge conducted 3 months post-immunization.

Main Results:

• 3-dose regimens showed VE ranging from 55% to 76%.
• RTS,S/AS01E and RTS,S/AS01B demonstrated comparable VE.
• The 2-dose regimen had significantly lower VE (29%).
• All regimens were well tolerated and immunogenic.

Conclusions:

• RTS,S/AS01E offers VE comparable to RTS,S/AS01B, supporting a universal formulation.
• 3-dose regimens are superior to the 2-dose regimen evaluated.