Measles antibodies and response to vaccination in children aged less than 14 months: implications for age of vaccination.

Passive immunity against measles decreases during the first months of life. The objective of this study was to determine titres of measles antibodies in children aged 9-14 months and their mothers before vaccination, and the children's response to vaccination. Blood samples were collected by capillary puncture before and 28 days after vaccination. Samples were obtained between February and June 2007 during an ongoing measles outbreak. Titres of specific measles IgG antibodies were determined by enzyme-linked immunosorbent assay. Seroconversion was defined as the presence of antibodies after vaccination in subjects without antibodies before vaccination. Maternal antibodies were present in 37·7% of all 69 children included and in 45·1% of children aged 9 months. Of the 51 children in whom a second sample was obtained, 31 (60·8%) were seronegative before vaccination and 61·3% seroconverted. Interference of maternal antibodies was 30%. Advancing the first dose of measles vaccination from 15 to 12 months is a correct strategy, given the increase in the time of susceptibility of infants to measles.