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

OBJECTIVE

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.

DESIGN

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.

SETTING

New South Wales, February-March 1995.

OUTCOME MEASURES: Documented measles immunization collected by interview survey and serologically defined immunity.

RESULTS

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).

CONCLUSIONS

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.