In a phase I double-blind study ( www.clinicaltrials.gov : NCT@ ) , healthy adults ( @-@ years ) were randomized ( @:@:@:@:@:@:@ ) to receive two doses of one of six investigational vaccine formulations @ months apart , or a single dose of the control @-valent pneumococcal polysaccharide vaccine ( @PPV ; Pneumovax@ , Sanofi Pasteur MSD ) followed by placebo .