Computer assessment of alternative rubella vaccination strategies in New Zealand.

Results from a dynamic computer model of rubella vaccination programmes indicate that consideration should be given to vaccinating all one-year-old girls and boys and revaccinating all girls at about 11 years of age, as well as continuing with the programme for susceptible women in the childbearing age group. With vaccine-induced immunity decaying at about 1% annually, the vaccination of 80 to 95% of all one-year-olds, 95% of 11 year old girls, and 5% of women aged 15 to 33 annually is expected to reduce congenital rubella syndrome deformities to less than 5% of the 1980 incidence by 1994, and to negligible levels thereafter. In comparison, continuation of the present scheme may reduce deformities to only 69% of 1980 levels by 1994 with a slow decline to 25% in 2010. (The 1980 levels used were computer generated to eliminate short-term fluctuations, and do not apply to actual figures from that year.) For convenience and better compliance, measles vaccine and the initial rubella vaccine may be given in combined form at 15 months without altering the effect of either. The rate of decay of immunity after vaccination is critically important in congenital rubella syndrome prediction, so that further accurate monitoring of immune status and congenital rubella incidence is essential.