An additional study objective was to assess the potential of virus shedding of the MV1-F4 vaccine (in parallel to that of the reference vaccine). In natural infection, MV can be isolated from urine up to 10 days after rash onset (Gresser and Katz 1960) , and viral RNA can be detected in PBMC and nasopharingeal specimens up to 100 days after rash onset (Riddell et al. 2007 ). The few known studies of shedding by attenuated MV vectors report detection of (Edmonston) viral RNA in buccal swabs from monkeys (after intravenous administration; Myers et al. 2007 ), but no detection in human urine or saliva (after intraperitoneal administration; Galanis et al. 2010) . Consistent with reports of detection of viral RNA from attenuated MV vaccine strains in human urine up to 14 days after vaccination (Rota et al. 1995) , we detected MV1-F4-derived RNA in urine at day 11. Infectious viral particles from MV vaccines have rarely been found in human throat or nasopharyngeal secretions, and there is only one reported case of isolation of (Schwarz) MV vaccine virus from throat swabs (Morfin et al. 2002) . While we detected viral RNA from both vaccines at the peak of viremia in a few samples such as throat and nasopharingal swabs, none of these contained infectious virus at a LOD of 10 CCID 50 /well (with 95 % probability). Therefore, transmission of MV1-F4 virus between persons is considered unlikely to occur, and has also never been documented previously for any of the current measles vaccines (WHO 2009) .