Measles outbreak in Burkina Faso, 2009: A case–control study to determine risk factors and estimate vaccine effectiveness

doi:10.1016/j.vaccine.2012.05.024

Vaccine

Volume 30, Issue 33, 13 July 2012, Pages 5000-5008

https://doi.org/10.1016/j.vaccine.2012.05.024 Get rights and content

Abstract

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.

Highlights

► We investigated a large (>54,000 cases) 2009 measles outbreak in Burkina Faso. ► In a case–control study, non-vaccination was the main risk factor for measles. ► Measles vaccine was effective in reducing risk of measles during the outbreak. ► Measles vaccination coverage was likely lower than reported national estimates. ► Main reasons provided for not receiving measles vaccination are described.

Introduction

Measles is a highly contagious disease associated with complications such as pneumonia, diarrhea, or encephalitis in approximately 30% of cases and case fatality ratios (CFRs) as high as 5–10% in developing countries [1], [2], [3], [4], [5]. In 2000, despite the availability of a safe and effective vaccine, measles caused an estimated 733,000 deaths worldwide; 371,000 (51%) of these were in Africa [6]. In 2001, the World Health Organization (WHO) Africa Region joined the global initiative to reduce measles deaths by 50% during 1999–2005 [6]. Strategies for measles mortality reduction recommended by WHO and United Nations Children's Fund (UNICEF) include (1) providing a first dose of measles vaccine to all children at age nine months or shortly after; (2) providing every child with a second opportunity to receive measles vaccine, either through a campaign or routine immunization; (3) establishing effective measles surveillance; and (4) improving measles case management [7]. Implementation of these strategies led to a significant decline in measles mortality globally and in Africa, where estimated measles deaths decreased 92%, from 371,000 to 28,000 during 2000–2008 [6].

However, further declines have been threatened by multiple outbreaks in Africa during 2009–2010, including a large outbreak in Burkina Faso in 2009 [8]. Burkina Faso, formerly Upper Volta, was one of the first countries to introduce measles vaccine and has conducted intermittent mass measles vaccination campaigns for children since the 1960s [9], [10], [11], [12], [13], [14], [15], [16]. Following the country's adoption of the WHO/UNICEF measles mortality reduction strategies, a nationwide “catch-up” campaign was conducted targeting children aged 9 months to 14 years in 2001 [17], and nationwide “follow-up” campaigns were conducted targeting children aged 9–59 months in 2004 and 2007. Based on post-campaign surveys, estimated coverage during these campaigns ranged from 96% to 97% nationwide [18], [19]. In addition to campaigns, routine measles immunization in Burkina Faso began in 1980 through the Expanded Programme on Immunization and consists of one dose of measles vaccine at age 9–11 months. WHO/UNICEF estimates of routine measles vaccination coverage have increased from 38% in 1985 to 75% during 2005–2008 (Fig. 1) [20].

Despite these immunization activities, Burkina Faso continued to experience periodic measles outbreaks, with a large outbreak in 2009. During May–August 2009, we conducted an investigation to describe the 2009 outbreak and outbreak response campaign, and a case–control study to determine risk factors for measles during the outbreak, estimate vaccine effectiveness (VE), and identify reasons for not receiving measles vaccination.

Section snippets

Field investigation

Measles vaccination coverage. Administrative estimates of vaccination coverage (number of doses administered by health care workers divided by the census-projected number of eligible children in the population) during routine immunization, previous immunization campaigns, and the 2009 outbreak response campaign were calculated using data provided by the Burkina Faso Ministry of Health (MOH).

Measles surveillance. Clinically diagnosed measles cases have been reportable to the Burkina Faso MOH

Measles epidemiology, 1996–2008

Before 2009, the largest documented measles epidemic in Burkina Faso occurred in 1996, with 32,415 reported cases (Fig. 1). During 1997–2005, annual outbreaks of 1077–8920 cases occurred, with peak transmission during January–June each year. In 2007, cases decreased to 150, an historic low. However, in 2008, cases increased to 1762 and transmission continued throughout the year and into 2009.

Measles outbreak, 2009

In total, 54,111 measles cases and 367 measles deaths were reported in 2009 through the aggregated

Discussion

Despite implementation of WHO-UNICEF measles mortality reduction strategies since 2001, including three nationwide immunization campaigns with >95% estimated coverage during 2001–2007 and increasing routine measles vaccination coverage, Burkina Faso experienced its largest measles outbreak on record in 2009. This outbreak was notable for its size and age distribution, with 35% of cases occurring in persons aged ≥15 years. The main risk factor for measles was lack of vaccination, and measles

Acknowledgments

This work was supported by the Burkina Faso Ministry of Health, World Health Organization (WHO), United Nations Children's Fund (UNICEF), and the United States Centers for Disease Control and Prevention (CDC). The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the CDC. This investigation would not have been possible without the support of numerous people in Burkina Faso and elsewhere. The authors would particularly like

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¹: Present address: Division of Global Migration and Quarantine, Centers for Disease Control and Prevention, United States.

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Published by Elsevier Ltd.

Measles outbreak in Burkina Faso, 2009: A case–control study to determine risk factors and estimate vaccine effectiveness

Abstract

Objective

Methods

Results

Conclusion

Highlights

Introduction

Section snippets

Field investigation

Measles epidemiology, 1996–2008

Measles outbreak, 2009

Discussion

Acknowledgments

Lancet

Vaccine

The clinical significance of measles: a review

J Infect Dis

Case-fatality rate during a measles outbreak in eastern Niger in 2003

Clin Infect Dis

Estimates of measles case fatality ratios: a comprehensive review of community-based studies

Int J Epidemiol

Global measles mortality 2000–2008

MMWR

Measles mortality reduction and regional elimination strategic plan 2001–2005

Measles outbreaks and progress toward measles preelimination – African region, 2009–2010

MMWR

Response of Volta children to jet inoculation of combined live measles, smallpox, and yellow fever vaccines

Bull World Health Organ

Response of Volta children to live attenuated measles virus vaccine

Bull World Health Organ

Sentinel for health: a history of the Centers for Disease Control

Standardization and mass application of combined live measles-smallpox vaccine in Upper Volta

Am J Epidemiol

Lessons learned. Rapid assessment: vaccination commando Burkina Faso

Mass measles vaccination in urban Burkina Faso, 1998

Bull World Health Organ

Measles incidence before and after mass vaccination campaigns in Burkina Faso

J Infect Dis

Measles vaccination coverage during poliomyelitis national immunization days in Burkina Faso, 1999

J Infect Dis

Migration as a risk factor for measles after a mass vaccination campaign, Burkina Faso, 2002

Int J Epidemiol

Evaluation de la campagne nationale de vaccination de masse contre la rougeole et la polio décembre 2004 au Burkina Faso