Optimal age for measles and mumps vaccination in Australia

Trivalent measles-mumps-rubella vaccine has recently replaced measles-mumps vaccine in Australia and is recommended as a single dose at the age of 12 to 15 months, with the exception of Aboriginal children in central Australia who are vaccinated at 9 months. The timing of measles vaccination has been controversial not only in Australia but also in the United States, where measles outbreaks continue to occur. This study aimed to determine seroconversion rates for measles-mumps vaccine in children aged 12 to 18 months and to make a recommendation for the timing of vaccination based on seroconversion rates and attack rates. The parents of 425 children aged 12 to 18 months gave consent for their children to have serum collected at the time of measles-mumps vaccination and three months later. The mean age at vaccination of the children who had two serum samples for measles and mumps antibody estimations was 13.9 months (mode, 13.1). The seroconversion rate for measles was 95% (314/329) (95% confidence interval (CI), 92.5% to 97.3%) and for mumps 97% (309/320) (95% CI, 93.8% to 98.1%). There were no statistically significant differences in the rates of seroconversion for measles or mumps related to age in months at the time of vaccination or in post-vaccination measles antibody titres related to age at vaccination. Post-vaccination mumps antibody titres tended to be lower in older vaccinees. None of the children who presented for vaccination had serological evidence of prior measles infection but five had evidence suggestive of prior mumps. As the seroconversion rates for measles and mumps vaccines were very high in these children it was concluded that no advantage resulted from delaying vaccination until 15 months and that the current National Health and Medical Research Council recommendations for vaccination at age 12 to 15 months should remain.