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

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.

This study involved a descriptive case-based record review of the national surveillance database for fever and rash illness.

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.

Multiple small outbreaks occurred simultaneously but were too brief to allow any particular genotype to establish itself as an endemic strain.