Measles outbreak in Burkina Faso, 2009: a case-control study to determine risk factors and estimate vaccine effectiveness.

Objective: We investigated a large measles outbreak that occurred in 2009 in Burkina Faso in order to describe the epidemic, assess risk factors associated with measles, and estimate measles vaccine effectiveness.

Methods: We reviewed national surveillance and measles vaccine coverage data, and conducted a case-control study in three geographic areas. Case-patients were randomly selected from the national case-based measles surveillance database or, when a case-patient could not be traced, were persons in the same community who experienced an illness meeting the WHO measles clinical case definition. Controls were matched to the same age stratum (age 1-14 years or age 15-30 years) and community as case-patients. Risk factors were assessed using conditional logistic regression.

Results: Lack of measles vaccination was the main risk factor for measles in all three geographic areas for children aged 1-14 years (adjusted matched odds ratio [aMOR] [95% confidence interval (CI)], 19.4 [2.4-155.9], 5.9 [1.6-21.5], and 6.4 [1.8-23.0] in Bogodogo, Zorgho, and Sahel, respectively) and persons aged 15-30 years (aMOR [95% CI], 3.2 [1.1-9.7], 19.7 [3.3-infinity], 8.0 [1.8-34.8] in Bogodogo, Zorgho, and Sahel, respectively). Among children aged 1-14 years, VE of any measles vaccination prior to 2009 was 94% (95% CI, 45-99%) in Bogodogo, 87% (95% CI, 37-97%) in Zorgho, and 84% (95% CI, 41-96%) in Sahel. Main reasons for not receiving measles vaccination were lack of knowledge about vaccination campaigns or need for measles vaccination and absence during vaccination outreach or campaign activities.

Conclusion: These results emphasize the need for improved strategies to reduce missed opportunities for vaccination and achieve high vaccination coverage nationwide in order to prevent large measles outbreaks and to continue progress toward measles mortality reduction.