This is a multicentre prospective Phase 4 study, to evaluate the safety of infants from 50 breastfeeding women, analyzable for the primary endpoint, after postpartum immunization with MMR vaccine.

During the screening period, eligibility will be determined based on the inclusion and exclusion criteria. Medical records of pregnant women will be screened by study investigators, who will then propose to the woman to participate in the study during a phone call or a follow-up visit. Screening visit could take place 4 months before delivery planned date up until the day of delivery.

The investigator will explain the study to the woman. A copy of the informed consent documents will be given to the woman for reading and for further information about the study (by email, by post, or personally).

If the woman is willing to participate in the study and after she had given her screening informed consent, a blood sample for measles serological analysis will be drawn.

After signing the consent, women meeting all the inclusion criteria and none of the exclusion criteria will be vaccinated in postpartum and before the exit of the maternity at day 0.

Each woman will have a blood draw at day 0 and breast milk samples as well as urine samples at the hospital at day 0 before vaccination.

Each included woman will also provide breast milk and urine home samples at days 7, 11 and 14 after vaccination. Reminder calls will be performed at days 7, 11 and 14 after vaccination.

Women will then be followed and vaccinated 8 weeks after the first vaccination, visit V1.

Each infant will be followed during 8 weeks. An optional blood sample for immunological analysis will be drawn at week 8 (visit v1). An informed consent form signed by the person(s) holding parental authority (both parents or mother only if the father has no parental authority) is needed for the infant to be included as well.

Diary cards will be used to follow the infant and the mother. If Infant and/or mother develop(s) suspected measles symptom(s), they will be evaluated by a study physician as soon as possible, preferably within 24 to 72 hours of acute measles symptom(s) onset.

In case of mother symptoms, the infant will be also seen by a physician during the mother's supplementary visit.

The visit at day 0 (V0) of the study will be performed at the maternity. The other visits, screening visit, V1 and supplementary visit (SV), will be performed either at the maternity or at the corresponding CIC if applicable. Home samples at 7, 11 and 14 days after vaccination will be directly sent at the laboratory of virology at Limoges. Home sampling can also be performed at the maternity or CIC according to their internal organization.