Rubella immunisation and immunity in a defined population.

The level of rubella immunity was measured in the population of Milton. Rubella antibody was measured by haemagglutination-inhibition in women and men aged 16 to 34 years. Details were sought of past rubella infection, immunisation and records of immunisation. Overall 11.3% of the women were not immune by the laboratory criterion. All women younger than 25 years had detectable rubella antibody, though 13.8% had low antibody levels not regarded as immune according to current criteria. These low antibody levels probably reflect the high prevalence of vaccine-induced immunity. Most of these women are likely to be immune and other methods of rubella screening are needed to identify the truly susceptible women. Women aged 32-34 years had the highest level of rubella susceptibility, 9% without any detectable rubella antibody. Although the Milton population may not be representative of the total New Zealand population, in this area there was an encouragingly low proportion of women who could be regarded as definitely susceptible to rubella.