Immunity in Persons Fully Vaccinated Against Measles, Mumps and Rubella and Responses to Booster Vaccination

Inclusion Criteria: * Aged 18-49 (inclusive) at the time of the study screening visit * Has received exactly two previous doses of MMR-containing vaccine at any point up to one calendar year prior to the study screening visit * Willing to receive a booster MMR vaccination as outlined in the study protocol * Able and willing to comply with all other study requirements (attend all study visits and provide blood, saliva, nasal wash samples at each visit as outlined) * Sufficient language (German or English) and cognitive skills * Provides written, informed consent to participate in the study Exclusion Criteria: * Acute respiratory or other infections (postpone baseline visit until resolved) * Receipt of any other vaccination less than 4 weeks prior to the baseline visit or intention to receive another vaccination within 4 weeks following the baseline visit * Previous hypersensitivity reaction following receipt of any MMR-containing vaccine or previous hypersensitivity reaction to any component of M-M-R-vaxPro * Pregnancy, lactation, or intention to become pregnant during the study * Individuals with confirmed or suspected immunosuppressive or immune-deficient state * Known current or chronic or severe disease * Receipt of blood or plasma transfusions, or administration of immune globulin (IG) less than 12 weeks prior to the baseline visit, or intention to receive IG within 4 weeks following the baseline visit * Any other significant disease, disorder, or finding which could p…