Epidemiological characteristics of a protracted and widespread measles outbreak in the Democratic Republic of Congo, 2018 - 2020

INTRODUCTION: measles is a highly contagious viral disease. Since 2011, the Democratic Republic of Congo (DR Congo) has had the first dose measles vaccination coverage of less than 80% according to the World Health Organization - United Nations International Children's Emergency Fund (WHO-UNICEF) coverage estimates, and measles mass vaccination coverage of less than the required coverage level of 95% by survey. Starting in August 2018, the country experienced an increase in measles case reports which continued through to early 2020. Epidemiological aspects of the outbreak are described in this article. METHODS: we analysed aggregate weekly passive surveillance data from the DR Congo for the years 2018 - 2020 to understand the trends of occurrence of suspected measles cases. We also analysed the measles case-based surveillance database to understand the epidemiological characteristics of confirmed cases of measles and rubella during the same period of time. RESULTS: a total of 458,156 suspected measles cases and 8,127 deaths were reported between 1(st) January 2018 and 31(st) December 2020, with the majority of cases and deaths reported in 2019. Only 2.9% of these cases were reported through the case-based surveillance system, with 31,639 cases being confirmed as measles by the laboratory, by epidemiological linkage and on clinical compatibility. Children less than 5 years of age were most affected with a cumulative incidence of 960 cases per 1,000,000 inhabitants. Only 41% of the confirmed cases were vaccinated. Maindombe and Tshopo provinces had the highest cumulative incidence levels. There was a distinct geographic progression of the outbreak between provinces during the course of the three years. A total of 1760 lab confirmed rubella cases were confirmed in various provinces among the cases investigated with blood specimens, 93% of whom were less than 15 years of age. CONCLUSION: the recent gaps in vaccination coverage, the age pattern of confirmed cases and the lack of vaccination history in the majority of cases is suggestive of failure to vaccinate as the likely cause of this large and protracted outbreak. Efforts to improve vaccination coverage and the measles surveillance system are needed in order to prevent the occurrence of future outbreaks and to avert measles-related deaths.