Seroresponse to the second measles vaccine dose at school entry in Qassim province, Saudi Arabia.

In 2001, the measles immunization schedule in Saudi Arabia was changed to 2 measles, mumps and rubella vaccine doses at 12 months and at 6 years. In this follow-up study we evaluated the seroresponse to the second measles dose before school entry. We recruited 138 children randomly from primary health care centres in Qassim; 124 children completed the study. Blood samples were collected before and 1 month after giving the second measles dose, before the age of 6 years. There was a statistically significant increase in the geometric mean titre of measles antibody, from 2205 m IU/mL before vaccination to 4723 mlU/mL after (P = 0.0001). The proportion of children with positive ELISA results increased fro++ 94.2% before vaccination to 99.2% after (P = 0.02), while the proportion with protective level (> or = 200 mlU/mL) increased from 97.1% before vaccination to 99.19% after (P = 0.21). The 2-dose measles immunization schedule can produce optimum protection at school entry if high vaccination coverage is guaranteed.