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Source: American Journal of Epidemiology
The World Health Organization guidelines for response to measles outbreaks in countries with mortality reduction goals recommend selective vaccination campaigns as an effective control measure. Nonselective campaigns, which do not require verification of vaccination status, facilitate swift implementation of the intervention. In addition, nonselective campaigns provide a second-dose opportunity for those who failed to seroconvert after the first dose. However, nonselective campaigns may preferentially favor those with high access to vaccination or willingness to be vaccinated and thus, the effective coverage of a nonselective campaign may be less than or equal to the population coverage of the campaign.
In this report, the authors evaluated the effective impact of the Ministry of Health/MSF campaign in Malawi in terms of the estimated coverage of the nonimmunized population. The authors then use simulation models to explore the efficiency of a nonselective campaign versus targeted vaccination in populations with heterogeneous access to mass vaccination campaigns. More details are available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3873105/
Abstract
Current mass vaccination campaigns in measles outbreak response are nonselective with respect to the immune status of individuals. However, the heterogeneity in immunity, due to previous vaccination coverage or infection, may lead to potential bias of such campaigns toward those with previous high access to vaccination and may result in a lower-than-expected effective impact. During the 2010 measles outbreak in Malawi, only 3 of the 8 districts where vaccination occurred achieved a measureable effective campaign impact (i.e., a reduction in measles cases in the targeted age groups greater than that observed in nonvaccinated districts). Simulation models suggest that selective campaigns targeting hard-to-reach individuals are of greater benefit, particularly in highly vaccinated populations, even for low target coverage and with late implementation. However, the choice between targeted and nonselective campaigns should be context specific, achieving a reasonable balance of feasibility, cost, and expected impact. In addition, it is critical to develop operational strategies to identify and target hard-to-reach individuals.