Background
MR, yellow fever
MEASLES, MUMPS, RUBELLA, YELLOW FEVER, DISEASE
Thirteen countries in the Americas and 34 in Africa are categorized as high risk for yellow fever (YF), either nationwide or within subnational areas. Almost all YF endemic countries administer both YF vaccine and measles-containing vaccine (MCV), i.e., measles, mumps, and rubella (MMR), measles-rubella (MR), or measles vaccine, via their national immunization programs. Because these are all live vaccines, the World Health Organization (WHO) recommends that they are administered at the same time (co-administered) or individually at least four weeks apart to prevent potential immune interference [Previous studies did not show an impact on reactogenicity and immunogenicity when measles and YF vaccines were co-administered [Since 2007, the Argentinean Ministry of Health (MOH) has recommended that YF vaccine be administered in part or all of the three northeastern provinces that are considered endemic for YF [From 2015 to 2018, the Argentinean MOH, Pan-American Health Organization (PAHO), and the U.S. Centers for Disease Control and Prevention (CDC) conducted a randomized controlled trial to evaluate the immune response to MMR and YF vaccines when co-administered to children aged 12–13 months. The study’s primary objective was to assess whether seroconversion against measles, rubella, mumps, and YF antigens following co-administration of MMR and YF vaccines was non-inferior to seroconversion when the vaccines were administered as the first vaccine in a series separated by four weeks (individual administration). Secondary objectives were to assess: (a) the magnitude of antibody responses to each antigen when the vaccines were co-administered compared with individual administration; (b) seroconversion and the magnitude of antibody responses when the vaccines were co-administered compared with administration as the second vaccine in a series separated by four weeks; and (c) seroconversion and the magnitude of antibody responses when the vaccines were administered as the second vaccine compared with administration as the first vaccine in a series separated by four weeks.