Factors determining the overlap between recipients of the first and second dose of measles vaccine in nineteen surveys.

Many countries schedule a second dose of measles-containing vaccine (MCV2) for children in their second year of life. The correlation between recipients of the first dose of measles-containing vaccine (MCV1) and MCV2 is poorly understood but is important for estimating population levels of measles immunity and for meeting elimination targets. Using data from 19 surveys from Demographic and Health Surveys (DHS) we computed the percentage of MCV1 recipients with subsequent MCV2 and of MCV2 recipients with previous MCV1. All countries included in our study recommended MCV1 in the first year of life and MCV2 in the second year of life. For 2 surveys we computed the variation of those percentages over the country's geographical regions. We computed adjusted odds ratios for the association of this percentage with age, sex, residency, mother's education, wealth and birth order. For most of the surveys, over 50% of MCV1 recipients received MCV2, but there was more than 30% MCV1 to MCV2 dropout in more than half of the surveys. The percentage of MCV1 recipients with MCV2 was statistically significantly higher if they received MCV1 below age 12 months and the percentage increased with increasing education status of the mother and higher income levels. A small number of MCV2 recipients were not found to have received MCV1, despite marked on record as having received MCV2 implies having previously received MCV1 (by definition of the survey data collection methodology). Our analyses have highlighted important shortfalls by age, country, mother's education and income status in the proportion of MCV1 recipients who subsequently receive MCV2. Targeting those differentials is essential for achieving the goals of measles elimination.