Mumps Outbreak: Bulgaria
There is an ongoing mumps outbreak in Bulgaria, with a total of 997 cases notified between 1 January and 18 March 2007. For comparison, only 22 cases were reported in the first 11 weeks of 2005, and 311 cases were registered in the same period in 2006.
Altogether, 608 cases were notified in 2005 and 919 cases were reported during 2006. An increase of the number of reported cases was noted already in 2006, and since the beginning of 2007 the number has continued to rise. The present mumps epidemic affects mostly teenagers and young adults.
More than 60% of the cases reported in 2007 occurred in patients aged 15-19 years, and about 20% in patients aged 20-24 years. To date, 112 out of 997 cases (11.2%) have been laboratory-confirmed. The outbreak investigation is still ongoing, but preliminary data indicate that the predominance of patients in age groups 15-19 and 20-24 years may be a result of a poor immunisation of these birth cohorts in general. About one third of patients aged 15-19 years have not been vaccinated at all, whereas more than half have received only one dose of monovalent mumps vaccine strain Leningrad 3, which has been shown to have a lower effectiveness.
Among the 20-24 year-old patients, over 90% have never been immunised against mumps. Vaccination against mumps in Bulgaria started in 1972, and a routine mumps immunisation programme was launched in 1976. However, different vaccine strains and vaccines have been used and different immunisation strategies implemented, including a suspension of mumps immunisation for almost four years during the period 1982-1986.
Due to the past changes in the immunisation programme and occasionally incomplete immunisation coverage, the conditions in which outbreaks can occur still exist, despite of the current up-to-date mumps immunisation strategy.