The validity of parental report of vaccination as a measure of a child's measles immunisation status

Objective: To determine the validity of parental report of vaccination as a measure of a child's measles immunisation status. Design: Cross-sectional survey. Setting: Four 24-hour medical centres in western Sydney. Patients: Parents of children aged 12-36 months were approached in the clinic waiting room. Of the 160 parents approached, 137 agreed to be interviewed and a successful venepuncture to yield a 2mL blood sample was achieved with 128 children. Main outcome measures: Measles IgG antibody, determined by means of an indirect ELISA, was compared with parental report of measles vaccination status by McNemar's χ² test. Results: Parental report significantly overestimates the immunisation status of children. Eighty-four per cent of the parents in the sample stated that their child had been vaccinated, but only 74% were immune (95% confidence interval, 65%-81%). A positive predictive value of 84% meant that only 84% of children who were reported to have been vaccinated were immune to measles. Further, of all those who were not immune to measles, only one half would have been identified by asking the parents. Failed seroconversion may have accounted for up to 70% of cases of non-immunity in children reported to have been vaccinated. Conclusions: Parental report is limited as a measure of a child's measles immunisation status.