 The study will simultaneously evaluate two primary objectives, one for noninferiority of the response to MV given with PRV co-primary objective 1 and one for noninferiority of the response to YFV given with PRV co-primary objective 2. For evaluation of co-primary objectives, venous blood specimens will be collected immediately prior to receipt of study vaccines and 4 weeks to plus 1 week later. Measles immunogenicity will be evaluated by measuring the MV neutralizing antibody seroconversion rates and geometric mean concentration GMCs 4 weeks post-vaccination. Yellow fever immunogenicity will be evaluated by measuring the yellow fever serum neutralizing antibody seroconversion rates and geometric mean titers GMTs 4 weeks post-vaccination 