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Mumps Outbreak Investigation, Eastern Province, Saudi Arabia in 2019


Mumps is an acute communicable viral disease characterized by fever and painful swelling of one or both parotid glands. Vaccination is the best way to prevent mumps. In the Kingdom of Saudi Arabia, the Ministry of Health (MOH) first introduced the mumps vaccination program in the mid-1970s. The effectiveness of two doses of mumps vaccine ranges from 79%-95%, with a median of 88%. This investigation aims to establish the existence of an increase in mumps cases in the Eastern Province, Saudi Arabia, 2018, and identify possible sources of infection.


We conducted a descriptive cross-sectional study of mumps cases. We include all mumps cases listed by the Dammam Preventive Medicine Department's database in 2018. We used data from their line list and structured questionnaires to conduct descriptive analyses using Microsoft Excel and SPSS.


During the year 2018, the Eastern Province report 53 laboratory-confirmed Mumps cases as compared to 9 laboratory-confirmed cases reported in 2017. Among the 53 laboratory diagnosed mumps cases: 41 cases (77%) were vaccinated, 10 cases (19%) did not know their vaccination history, and 2 cases (4%) were not vaccinated. Twenty-nine cases vaccinated during 2018 and developed symptoms within one incubation period (12-25 days) of vaccination


After investigating this outbreak, it became clear to us that most cases (55%) occurred within one incubation period of vaccination. An inadequately inactivated vaccine is one of the possible cause of increased cases than expected. Other possible reasons behind the increase in cases include waning immunity or a genetic mismatch of vaccine and wild-type strains.