The Minicommunity Design to Assess Indirect Effects of Vaccination

Abstract

We propose the minicommunity design to estimate indirect effects of vaccination. Establishing indirect effects of vaccination in unvaccinated subpopulations could have important implications for global vaccine policies. In the minicommunity design, the household or other small transmission unit serves as the cluster in which to estimate indirect effects of vaccination, similar to studies in larger communities to estimate indirect, total, and overall effects. Examples from the literature include studies in small transmission units to estimate indirect effects of pertussis, pneumococcal, influenza, and cholera vaccines. We characterize the minicommunity design by several methodologic considerations, including the assignment mechanism, ascertainment, the role of transmission outside the transmission unit, and the relation of the size of the transmission unit to number of people vaccinated. The minicommunity study for indirect effects is contrasted with studies to estimate vaccine effects on infectiousness and protective effects under conditions of household exposure within small transmission units. The minicommunity design can be easily implemented in individually randomized studies by enrolling and following-up members of households of the randomized individuals. The methodology for the minicommunity design for estimating indirect effects of vaccination deserves much future research.

Figure 1

Sample of households used in the analysis in a minicommunity study. All households are included, avoiding post-randomization selection bias. The larger shaded circles represent households. Each household has three individuals in it, one of whom, indicated in white, is in an individually randomized, controlled trial of a vaccine (v) versus control (c). The smaller circles represent uninfected people, the stars represent infected people.

Figure 2

Sample of households used to estimate vaccine efficacy for infectiousness. As in Figure 1, the larger shaded circles represent households. Each household has three individuals in it, one of whom, indicated in white, is in an individually randomized, controlled trial of a vaccine (v) versus control (c). The smaller circles represent uninfected people, the stars represent infected people. The large Xs indicate that a household is not included in the analysis. One could include only households in which the first case in the household was in the randomized trial.