Participants were randomly assigned ( 1:1:1 ) at first vaccination by block randomisation with minimisation by centre to receive three doses of RTS , S/AS01 at months 0 , 1 , and 2 and a booster dose at month 20 ( R3R group ) ; three doses of RTS , S/AS01 and a dose of comparator vaccine at month 20 ( R3C group ) ; or a comparator vaccine at months 0 , 1 , 2 , and 20 ( C3C [ control group ] ) .