Warning: these figures indicate the number of cases found in the data file. They cannot be interpreted as summary statistics of the population of interest.
A child receives a number of preventative immunizations in his/her first few years (e.g. polio, DPT, measles, etc.) For immunizations to be fully effective, the child should receive the entire course of vaccinations. For the purposes of this questions, however, all we are interested in is whether or not the child has ever received any immunization, i.e. regardless of whether the course was completed or not.