RESUMEN
The present study was conducted on 2114 infants divided into different age groups ranging from 6-18 months. All studied infants were subjected to full history taking, thorough clinical examination and laboratory investigation for semiquantitative measurement of mumps IgG by ELISA technique. The study revealed that maternally acquired mumps seropositivity wanes out gradually reaching its nadir level at the age of 12-13 months. Therefore, infants in this age period have a greater risk to develop mumps infection with either higher morbidity or mortality. Hence, the study recommended that MMR vaccination should be adopted at 12-13 months of age in the expanded program of immunization in Egypt as being the time of waning out of passively acquired mumps IgG