Measles incidence before and after mass vaccination campaigns in Burkina Faso

Synthesis of Evidence to Characterize National Measles and Rubella Exposure and Immunization Histories

Population immunity depends on the dynamic levels of immunization coverage that countries achieve over time and any transmission of viruses that occur within the population that induce immunity. In the context of developing a dynamic transmission model for measles and rubella to support analyses of future immunization policy options, we assessed the model inputs required to reproduce past behavior and to provide some confidence about model performance at the national level. We reviewed the data available from the World Health Organization (WHO) and existing measles and rubella literature for evidence of historical reported routine and supplemental immunization activities and reported cases and outbreaks. We constructed model input profiles for 180 WHO member states and three other areas to support disease transmission model development and calibration. The profiles demonstrate the significant variability in immunization strategies used historically by regions and member states and the epidemiological implications of these historical choices. The profiles provide a historical perspective on measles and rubella immunization globally at the national level, and they may help immunization program managers identify existing immunity and/or knowledge gaps.

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.

The dynamics of measles in sub-Saharan Africa

Although vaccination has almost eliminated measles in parts of the world, the disease remains a major killer in some high birth rate countries of the Sahel. On the basis of measles dynamics for industrialized countries, high birth rate regions should experience regular annual epidemics. Here, however, we show that measles epidemics in Niger are highly episodic, particularly in the capital Niamey. Models demonstrate that this variability arises from powerful seasonality in transmission-generating high amplitude epidemics-within the chaotic domain of deterministic dynamics. In practice, this leads to frequent stochastic fadeouts, interspersed with irregular, large epidemics. A metapopulation model illustrates how increased vaccine coverage, but still below the local elimination threshold, could lead to increasingly variable major outbreaks in highly seasonally forced contexts. Such erratic dynamics emphasize the importance both of control strategies that address build-up of susceptible individuals and efforts to mitigate the impact of large outbreaks when they occur.

Time is of the essence: exploring a measles outbreak response vaccination in Niamey, Niger

The current World Health Organization recommendations for response during measles epidemics focus on case management rather than outbreak response vaccination (ORV) campaigns, which may occur too late to impact morbidity and mortality and have a high cost per case prevented. Here, we explore the potential impact of an ORV campaign conducted during the 2003-2004 measles epidemic in Niamey, Niger. We measured the impact of this intervention and also the potential impact of alternative strategies. Using a unique geographical, epidemiologic and demographic dataset collected during the epidemic, we developed an individual-based simulation model. We estimate that a median of 7.6% [4.9-8.9] of cases were potentially averted as a result of the outbreak response, which vaccinated approximately 57% (84563 of an estimated 148600) of children in the target age range (6-59 months), 23 weeks after the epidemic started. We found that intervening early (up to 60 days after the start of the epidemic) and expanding the age range to all children aged 6 months to 15 years may lead to a much larger (up to 90%) reduction in the number of cases in a West African urban setting like Niamey. Our results suggest that intervening earlier even with lower target coverage (approx. 60%), but a wider age range, may be more effective than intervening later with high coverage (more than 90%) in similar settings. This has important implications for the implementation of reactive vaccination interventions as they can be highly effective if the response is fast with respect to the spread of the epidemic.

Characterization of immune responses induced by intramuscular vaccination with DNA vaccines encoding measles virus hemagglutinin and/or fusion proteins

Measles virus (MV) hemagglutinin (MV-H) and fusion (MV-F) proteins induce plaque reduction neutralizing (PRN) antibodies and cell-mediated immune responses that protect against clinical measles. DNA vaccines that encode MV-H and MV-F are being investigated as a new generation of measles vaccine to protect infants too young to receive currently licensed attenuated measles vaccines. However, it is unclear whether DNA vaccines encoding both MV-H and MV-F act synergistically to induce stronger immunity than immunization with plasmids encoding MV-H or MV-F alone. To address this question, we generated Sindbis virus-based pSINCP DNA vaccines that encode either MV-H or MV-F alone or bicistronic or fusion system vectors that encode both MV-H and MV-F (to mimic MV infection where both MV-H and MV-F proteins are expressed by the same mammalian cell). Mice immunized with DNA vaccine encoding MV-H alone developed significantly greater PRN titers than mice immunized with bicistronic constructs. Interestingly, the presence of MV-F in the bicistronic constructs stimulated serum MV-specific immunoglobulin G of reduced avidity. By contrast, mice immunized with bicistronic constructs induced equivalent or higher levels of MV-specific gamma interferon responses than mice immunized with DNA vaccine encoding MV-H alone. These data will help guide the design of DNA-based MV vaccines to be used early in life in a heterologous prime-boost strategy.

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

BACKGROUND

Shortly after a measles supplementary immunization activity (SIA) targeting children from 9 months to 14 years of age that achieved high coverage, Burkina Faso had a large, serologically confirmed measles outbreak. To investigate the causes of this first reported failure of a widely successful measles control strategy we conducted a case-control study.

METHODS

Serologically confirmed measles cases aged > or =9 months at the time of the SIA in 6 heavily affected districts were frequency matched on age to 3 controls recruited from people frequenting health centres in the same districts.

RESULTS

Between January and July 2002, 1287 measles cases were reported throughout Burkina Faso. Of the 707 cases that were serologically confirmed, 358 (51%) were from 9 months to 14 years of age and 265 (37%) were > or =15 years of age. Among cases and controls from 9 months to 14 years of age significant risk factors for measles were lack of measles vaccination and, in the unvaccinated, recent travel to Cote d'Ivoire. Of the recent measles cases in Cote d'Ivoire 54% were there when exposed to measles. Among adults, risk factors included non-vaccination and the lack of school attendance during childhood. Vaccine effectiveness was estimated to be 98%.

CONCLUSIONS

Migration of children between Cote d'Ivoire and Burkina Faso played a major role in the failure of the SIA to interrupt measles transmission. Synchronization of measles control activities should be a high priority in countries with regions where much migration occurs.

Impact of alternative approaches to accelerated measles control: experience in the African region, 1996-2002

From 1996 to 2000, several African countries accelerated measles control by providing a second opportunity for measles vaccine through supplemental campaigns. Fifteen countries completed campaigns in children aged 9 months to 14 years. Seven countries completed campaigns in children aged 9-59 months. In almost all countries that conducted campaigns in children aged 9 months to 14 years, measles deaths were reduced to near zero. In six countries, near-zero measles mortality has been maintained for 4-6 years. Supplemental immunization in children <5 years old was only partially effective (range, 0-67%) in reducing mortality. Measles cases decreased by 50% when routine vaccination coverage increased from 50% to 80%. Initial measles campaigns in children aged 9 months to 14 years, follow-up campaigns in those aged 9-59 months every 3-5 years, and increased routine coverage to 80% will be needed to reduce and maintain measles deaths in African countries at near zero.

Limited diversity of measles field isolates after a national immunization day in Burkina Faso: progress from endemic to epidemic transmission?

Despite recent National Immunization Days in Burkina Faso, the rural province of Houët reported >400 measles cases in 2001 (82% not vaccinated). Phylogenetic analysis of 58 measles virus field isolates plus the first sequences from the Democratic Republic of the Congo and the Republic of Congo are reported. All viruses were genotype B3, which is common in the region. In Houët, there were two geographically confined genetic variants, suggesting two independent importation events. Strain diversity in Houët (1.5%) and the Congos was limited in comparison with Ibadan, Nigeria (4.6%), where measles is endemic. Strain variability, assessed by heteroduplex mobility assay, confirmed these findings. Despite large local pools of susceptible persons even after several rounds of vaccination, the limited strain diversity suggests that parts of rural Burkina Faso may be moving from an endemic to an epidemic transmission pattern of measles virus.