Vaccinoprophylaxis of mumps using mumps vaccine, strain Sofia 6, in Bulgaria.

A mumps vaccine, using strain Sofia 6 prepared in guinea-pig kidney primary cell cultures, was gradually introduced in Bulgaria to vaccinate 1- to 12-year-old children between 1972 and 1976. It was included in the national vaccine programme in 1977. The vaccine showed a slight reactogenicity, a good immunogenicity and a high epidemiological efficacy. Due to the increased morbidity of mumps, revaccination was carried out in 4- to 12-year-old children in 1982. A high level of side-effects, mainly meningitis, was registered, and led to suspension of the mumps vaccine in Bulgaria.