Epidemiology of measles clusters/outbreaks during 2016-2017 in Oman.

Objectives: The epidemiology of measles in Oman has shown a decreasing trend since the introduction of vaccines with high coverage, even at the district level. Oman achieved elimination status in 2019. Currently, measles epidemiology is characterized by a small number of imported and importation-related cases with limited spread in the community. The main aim of the study is to describe the epidemiology of major measles outbreaks in Oman during 2016-2017. Methods: This study involved a descriptive case-based record review of the national surveillance database for fever and rash illness. Results: A total of 231 measles cases were reported during 2016-2017. Of the reported cases, 209 (90.5%) were laboratory-confirmed, 16 (6.9%) were clinically compatible, and six (2.6%) were epidemiologically linked cases. There were 10 clusters/outbreaks comprising 191 cases (185 laboratory-confirmed cases and six epidemiologically linked to a confirmed case) in various governorates of Oman during 2016-2017. The study population had a mean age of 11.4 years, ranging from 0.2 to 55 years across the outbreaks. The median age was 9 months. Approximately 50.7% of the cases involved infants aged ≤12 months, who were not yet eligible for measles vaccination. The second most affected age group were individuals aged 20-35 years. The largest and the longest cluster during 2016-2017 occurred in Dhofar and Sharqiyah, involving 90 cases attributed to genotype B3, which lasted for 32 weeks. Conclusions: Multiple small outbreaks occurred simultaneously but were too brief to allow any particular genotype to establish itself as an endemic strain.