Yellow fever vaccination coverage heterogeneities in Luanda province, Angola

Although the latest yellow fever outbreak appears to be approaching a close, nearly 2000 suspected and confirmed cases have been reported in Angola since December, 2015.1 Aggressive vaccination campaigns, coordinated by the Angolan Ministry of Health (MOH) and WHO in the highly affected Luanda province, have been crucial to outbreak mitigation; as of April 10, 2016, 5·9 million (90%) individuals of the province-level target population (6·6 million) were reported to have been vaccinated.1

However, pockets of undervaccination pose a potential challenge for disease elimination. Eight of 12 districts in Luanda province vaccinated less than half of their district-level target populations.1 In addition to these heterogeneities in geographical vaccination coverage, susceptibility among individuals throughout the target population (ie, Luanda province) is likely to be heterogeneous as well. For example, because yellow fever is a vector-borne disease, members of the target population who work outdoors might possess a higher risk of infection than those who do not; as a result, the population that is truly susceptible to yellow fever only comprises a fraction of the target population.

If the truly susceptible fraction of the target population is over-represented in currently undervaccinated districts, the outbreak could continue to smoulder, despite a 90% province-level vaccination rate.