Figure 2.

Comparison of vaccine effect estimates and power of individually randomized controlled trials (iRCTs) and cluster-randomized controlled trials (cRCTs), showing vaccine effect estimates (A), design effect (B), and power (C), analyzed using either a shared gamma-frailty model or a Cox proportional hazards model with robust standard error (SE) estimates. The data are simulated. The incidence rate of importations into an average community is 0.5 cases/year, the vaccine efficacy is 60%, and other parameters are the baseline values listed in Table 1.