Increase in congenital rubella occurrence after immunisation in Greece: retrospective survey and systematic review How does herd immunity work?

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Abstract
Objective: To describe the events leading to the epidemic of congenital rubella syndrome in Greece in 1993 after a major rubella epidemic. Design: Retrospective survey and systematic review. Setting: Greece (population 10 million), 1950-95. Subjects: Children, adolescents, and women of childbearing age. Results: Around 1975 in Greece the measles, mumps, and rubella vaccine started being given to boys and girls aged 1 year without policies to attain high vaccination coverage and to protect adolescents and young women During the 1980s, vaccination coverage for rubella remained consistently below 50%, and the proportion of pregnant women susceptible to rubella gradually increased. In 1993 the incidence of rubella in young adults was higher than in any previous epidemic year. The epidemic of congenital rubella that followed, with 25 serologically confirmed cases (24.6 per 100 000 live births), was probably the largest such epidemic in Greece after 1950. Conclusions: With low vaccination coverage, the immunisation of boys and girls aged 1 year against rubella carries the theoretical risk of increasing the occurrence of congenital rubella. This phenomenon, which has not been previously reported, occurred in Greece. Objective: To describe the events leading to the epidemic of congenital rubella syndrome in Greece in 1993 after a major rubella epidemic. Design: Retrospective survey and systematic review. Setting: Greece (population 10 million), 1950-95. Subjects: Children, adolescents, and women of childbearing age. Results: Around 1975 in Greece the measles, mumps, and rubella vaccine started being given to boys and girls aged 1 year without policies to attain high vaccination coverage and to protect adolescents and young women During the 1980s, vaccination coverage for rubella remained consistently below 50%, and the proportion of pregnant women susceptible to rubella gradually increased. In 1993 the incidence of rubella in young adults was higher than in any previous epidemic year. The epidemic of congenital rubella that followed, with 25 serologically confirmed cases (24.6 per 100 000 live births), was probably the largest such epidemic in Greece after 1950. Conclusions: With low vaccination coverage, the immunisation of boys and girls aged 1 year against rubella carries the theoretical risk of increasing the occurrence of congenital rubella. This phenomenon, which has not been previously reported, occurred in Greece.