RESUMEN
To evaluate the sero-response to measles component of the first measles, mumps MMR dose given at 12 months by measuring measles antibody before and one month after the vaccination. A follow-up study where, 57 children at the age of 12 months were recruited randomly from the Primary Health Care Centers in Qassim, Saudi Arabia using a multistage sampling techniques. Fieldwork was conducted from October until December 2006. Blood samples were collected to measure measles IgG antibody before, and one month after giving MMR using enzyme linked immunosorbent assay. Data were compared before and after vaccination using geometric mean titer GMT and seroconversion. In the 57 infants, positivity rate increased significantly from 3.5% [2/57] pre-vaccination to 100% one month after p=0.0001, and with a sero-conversion of 96.5% [55/57]. Also, GMT increased significantly from 0.014-2.172 IU/ML, after vaccination p=0.0001. Sero conversion and GMT are significantly high after the first MMR given at 12 months and this is supported by the surveillance data in Qassim