Serogroup A Meningococcal Conjugate Vaccine Coverage After the First National Mass Immunization Campaign — Burkina Faso, 2011

In December 2010, Burkina Faso became the first country to introduce PsA-TT (MenAfriVac), a new serogroup A meningococcal conjugate vaccine developed to eliminate epidemic meningitis in sub-Saharan Africa, via a national mass-immunization campaign. This campaign targeted persons aged 1–29 years, approximately 70% of the 16 million residents of the country. More than 11 million vaccine doses were administered in a 10-day period, for an estimated administrative coverage* of 102.6% (1). Accurate vaccination coverage estimates are critical for programmatic evaluation, identification of undervaccinated subpopulations, and for measurement of the impact of PsA-TT on serogroup A disease and carriage. In December 2011, the Burkina Faso Ministry of Health, in collaboration with CDC, conducted a stratified cluster survey to obtain regional and age-group–specific vaccination coverage estimates among campaign-eligible persons. National coverage was 95.9% (74.3% with vaccination card, 21.6% by recall), and coverage in the 13 regions of Burkina Faso ranged from 90.8% to 98.3%. Coverage was 97.0% in children aged 2–5 years, 97.4% in those aged 6–15 years, and 93.4% in those aged 16–30 years. The results of this survey demonstrate successful introduction of a new vaccine in Burkina Faso through a mass immunization campaign, the first step in a strategy aimed at rapidly interrupting transmission and carriage of serogroup A Neisseria meningitidis before introduction of the vaccine into national routine immunization programs. With phased introduction of PsA-TT planned through 2016 (2) in Africa's "meningitis belt,"† lessons learned from the Burkina Faso experience will help guide successful introduction of serogroup A meningococcal conjugate vaccine elsewhere.

A national survey was conducted during December 17–27, 2011, using a stratified cluster sampling scheme to assess PsA-TT coverage achieved by the mass immunization campaign implemented during December 6–15, 2010, in Burkina Faso. The sampling frame for a target population of persons aged 2–30 years (those aged 1–29 years in December 2010) was derived from 2011 population estimates projected from the 2006 national census. Strata were defined by the 13 administrative regions. Twenty-five enumeration areas, which are the smallest geographic units into which the country is divided for the purposes of a census, were selected from each stratum in the first stage using probability proportional to size. In each enumeration area, field teams demarcated the boundaries of the enumeration area, enumerated all the households, and systematically selected 20 households by calculation of a sampling interval. All campaign-eligible persons residing in selected households were included. The sample size of 500 households per stratum was calculated to provide regional estimates for three age groups (2–5 years, 6–15 years, and 16–30 years) with +/-8% precision, assuming 80% coverage, 95% confidence intervals (CIs), a design effect§ of two, and a 5% nonresponse rate.

A questionnaire was administered to the head of each of the consenting retained households to capture demographic and socioeconomic information for the household. Vaccination status, modes of communication regarding the vaccination campaign, and reasons for nonvaccination were recorded by direct interview with eligible household members, or by head of household or other parent for children too young to respond. Receipt of vaccination was documented by a vaccination card designed specifically for this campaign, or by recall. Additionally, residency in Burkina Faso during the 2010 campaign was recorded to obtain campaign coverage estimates and 2011 population coverage estimates, accounting for migration to and from bordering countries. Before survey implementation, a pilot study and formal training of field teams were conducted. Each field team consisted of two interviewers and a supervisor who were under the direction of a regional supervisor. The sample was assumed to be self-weighting within each stratum. For the national estimates, stratum-specific weights were included. Variance estimates using Taylor series linearization to account for the survey design were used to calculate 95% CIs.

A total of 23,890 eligible persons from 6,455 households were surveyed; 6,434 (99.7%) of retained households consented to participation in the survey. Of enrolled consenting persons, 23,577 (99.2%) resided in Burkina Faso during the 2010 campaign. The 2011 estimated coverage among all surveyed persons did not differ significantly from estimated coverage among those residing in Burkina Faso during the 2010 campaign, and thus only results from those residing in Burkina Faso during the campaign are reported. National coverage was estimated to be 95.9%, with coverage documented by vaccination card for 74.3% and by recall only for 21.6%. Estimated coverage was >90% in all regions, with the lowest coverage in the most populous Centre region (90.8%) and highest in the Centre-Ouest region (98.3%) (Table 1). Coverage was 97.0% in children aged 2–5 years, 97.4% in those aged 6–15 years, and 93.4% in persons aged 16–30 years. Coverage was 96.1% in females and 95.8% in males. Highest coverage was in females aged 2–5 years (97.7%), and lowest in males aged 16–30 years (93.0%) (Table 2). Among the 775 unvaccinated persons with a known reason for nonvaccination, the most commonly cited reasons were as follows: not informed (44.2%), absence (16.4%), no vaccine available at site (7.6%), and did not know the location of the vaccination clinic (6.4%). The most commonly reported modes of campaign communication were criers (social mobilizers) (36.8%), community health workers (24.0%), family (13.4%), and school (9.6%).

Reported by

Isaïe Médah, MD, Dénis Yélbeogo, MD, Jean Ludovic Kambou, MD, Direction de la Lutte Contre la Maladie, Ministère de la Santé du Burkina Faso. Kathleen Wannemuehler, PhD, James L. Goodson, MPH, Brendan Flannery, PhD, Global Immunizations Div, Center for Global Health; Amanda Cohn, MD, Ryan T. Novak, PhD, Thomas Clark, MD, Nancy E. Messonnier, MD, Div of Bacterial Diseases, National Center for Immunization and Respiratory Diseases; Sarah A. Meyer, EIS Officer, CDC. Corresponding contributor: Sarah A. Meyer, smeyer@cdc.gov, 404-639-3158.

Editorial Note

In the meningitis belt of sub-Saharan Africa, serogroup A meningococcal meningitis is a major cause of death and disability. Major epidemics occur every 5–12 years, with hundreds of thousands of cases and a case-fatality ratio of >10% (3). During 2010–2011, PsA-TT was introduced into the hyperendemic countries of Burkina Faso, Mali, and Niger through mass campaigns, at a cost of $0.40 per dose. As of December 2012, 100 million persons had been vaccinated in 10 countries, and introduction is planned in a further 16 countries by the end of 2016.

As the first country to introduce PsA-TT on a national scale, Burkina Faso achieved >90% coverage in all regions, target age groups, and both sexes. These results demonstrate that mass vaccination of a large proportion of the population is an effective strategy to rapidly achieve high vaccine coverage. The scope of this campaign is unprecedented; previous measles and yellow fever campaigns have only targeted children aged <15 years or affected or at-risk districts, making this PsA-TT campaign the largest and most successful immunization activity in Burkina Faso's history (1). Particularly impressive is the high coverage in persons aged 16–30 years, especially among males, and the high card retention seen in all age groups 1 year after the immunization campaign.

Overall administrative coverage estimates in the six countries that introduced PsA-TT during 2010–2011 were >90% in each country (4,5). However, administrative coverage estimates do not reliably provide valid estimates of coverage; therefore, population-based coverage surveys are needed to identify areas of potential undervaccination and population susceptibility (6). The rigorous sampling methods and large sample size in this survey provide a representative and precise estimate of PsA-TT coverage in Burkina Faso. Although the survey was conducted 1 year after the immunization campaign, the majority of persons had proof of vaccination by card. The potential for recall bias among those who reported vaccination by recall only might be offset by the high-profile nature of the disease and the vaccination campaign in Burkina Faso. In addition, because only the PsA-TT campaign was conducted during this period, vaccination with PsA-TT is unlikely to be confused with other vaccinations. Most persons living in Burkina Faso during the survey also reported living in Burkina Faso during the vaccination campaign; however, the campaign and survey were both during the start of the dry season in December, thus the effect of migration of potentially unvaccinated persons during other seasons is unknown.

A remarkable early impact of PsA-TT has been demonstrated in Burkina Faso. In the 2 years since vaccine introduction, enhanced meningitis surveillance has detected only one confirmed case of serogroup A meningococcal meningitis in an unvaccinated Burkina Faso resident and no cases in vaccinated persons, representing a 99.8% risk reduction (7) (Direction de la Lutte Contre la Maladie. Burkina Faso Ministry of Health, unpublished data, 2012). This substantial reduction in disease among all age groups, including the 30% of the population outside of the target age for vaccination, not only indicates excellent early vaccine effectiveness, but also is suggestive of herd immunity.

Achievement of high vaccination coverage in Burkina Faso demonstrates that coordinated preparation through microplanning, community engagement and mobilization, and development of a comprehensive communication plan are critical to successful vaccination campaigns (1). To eliminate epidemics of serogroup A meningococcal meningitis, high population immunity is necessary throughout the meningitis belt. After initial campaigns targeting persons aged 1–29 years, maintenance of high PsA-TT coverage through protection of each birth cohort is necessary, either by routine immunization services or periodic mass campaigns. When routine immunization or periodic mass campaigns will need to be initiated is not yet known. Reliable vaccination coverage estimates will continue to be needed to monitor and evaluate the introduction of this new vaccine, and to measure the impact of vaccination on achieving the goal of eliminating epidemic meningitis in the region.

Acknowledgments

Souleymane Sanou, MD, Maurice Hien, MD, Ministère de la Santé du Burkina Faso, Mamoudou Djingarey, MD, Fabien Diomande, MD, Meningitis Vaccine Project. Flavien Ake, CDC.

References

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