Measles vaccine effectiveness in standard and early immunization strategies, Niger, 1995

BACKGROUND.An Expanded Programme on Immunization was started in late 1987 in Niger, including vaccination against measles with one dose of standard titer Schwarz vaccine given to infants after 9 months of age. During epidemics an early two-dose strategy was implemented (one dose between 6 and 8 months and one dose after 9 months). From January 1, 1995, until May 7, 1995, 13 892 measles cases were reported in Niamey, Niger. METHODS.A retrospective cohort study was conducted in a crowded area of Niamey at the end of the outbreak to assess the effectiveness of measles vaccine in standard (after 9 months) and early (before 9 months) immunization strategies under field conditions. RESULTS.Highest measles incidence rates were observed among children