Measles immunity and immunization status in under-5-year-old children in New South Wales: a population-based study.

Abstract

To estimate the proportion of 1-4-year-old New South Wales children immune to measles and compare the documented immunization history with serologically defined immune status. Population based seroprevalence survey piggybacked onto the National Survey of Lead in Children. Immune status was determined by two different enzyme immunoassays on plasma samples from subjects. New South Wales, February-March 1995. Documented measles immunization collected by interview survey and serologically defined immunity. Of 689 survey subjects, 430 (62.4%) provided a blood sample. Adequate plasma remained for both assays for 347 children, of whom 279 (80.4%) were immune by both assays. Parents of 330 stated that their children were immunised, of whom 211 (63.9%) were able to produce corroborating records. Of these 211 subjects, 178 (84.4%) were immune compared to 87 (76.3%) of 114 without records (P = 0.07). We estimate the prevalence of true measles immunity in 1-4-year-old NSW children to be only 80%, a level inadequate to prevent outbreaks of measles in urban populations. Both long term and immediate strategies are required to increase the prevalence of immunity among NSW children; these may include lowering the age of the routine second measles dose and mounting a mass measles immunisation campaign to include preschool aged children.