Measles outbreaks in displaced populations: a review of transmission, morbidity and mortality associated factors

Background: Measles is a highly contagious infectious disease with a significant public health impact especially among displaced populations due to their characteristic mass population displacement, high population density in camps and low measles vaccination coverage among children. While the fatality rate in stable populations is generally around 2%, evidence shows that it is usually high among populations displaced by disasters. In recent years, refugees and internally displaced persons have been increasing. Our study aims to define the epidemiological characteristics and risk factors associated with measles outbreaks in displaced populations. Methods: We reviewed literature in the PubMed database, and selected articles for our analysis that quantitatively described measles outbreaks. Results: A total of nine articles describing 11 measles outbreak studies were selected. The outbreaks occurred between 1979 and 2005 in Asia and Africa, mostly during post-conflict situations. Seven of eight outbreaks were associated with poor vaccination status (vaccination coverage; 17-57%), while one was predominantly due to one-dose vaccine coverage. The age of cases ranged from 1 month to 39 years. Children aged 6 months to 5 years were the most common target group for vaccination; however, 1622 cases (51.0% of the total cases) were older than 5 years of age. Higher case-fatality rates (>5%) were reported for five outbreaks. Consistent factors associated with measles transmission, morbidity and mortality were vaccination status, living conditions, movements of refugees, nutritional status and effectiveness of control measures including vaccination campaigns, surveillance and security situations in affected zones. No fatalities were reported in two outbreaks during which a combination of active and passive surveillance was employed. Conclusion: Measles patterns have varied over time among populations displaced by natural and man-made disasters. Appropriate risk assessment and surveillance strategies are essential approaches for reducing morbidity and mortality due to measles. Learning from past experiences of measles outbreaks in displaced populations is important for designing future strategies for measles control in such situations.