REACHING HARD-TO-REACH INDIVIDUALS: NONSELECTIVE VERSUS TARGETED OUTBREAK RESPONSE VACCINATION FOR MEASLES

Tuesday, 22nd of October 2013

[source]American Journal of Epidemiology[|source]

In this article, the authors assert that the impact of a supplemental mass vaccination campaign is variable and may be lower than expected because of population heterogeneity in immunity and the naive presumption that outbreak response vaccination campaign is nonselective with respect to the immune status of individuals. The authors argue that in highly vaccinated populations, targeted campaigns achieve higher impacts, even when target coverage is low and implementation is late, and they are the most effective strategy. No presumptions are made that selective vaccination response to outbreaks are easy or logistically offer any less a challenge.

Targeted (selective) outbreak vaccination response may introduce additional trade-offs; although a targeted campaign may vaccinate immune individuals, if not well implemented, it may also result in fewer people being immunized. Irrespective of the strategy selected, reinforcement of surveillance and investigation of local epidemiologic data to guide the decision are essential. The article concludes that developing operational strategies to identify and target individuals and subpopulations with low levels of vaccination is paramount to ensuring the effectiveness of selective vaccination response interventions. More details are available at:  http://aje.oxfordjournals.org/content/early/2013/10/15/aje.kwt236.full

 

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 non-vaccinated 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.