FIG. 3.

Two potential two-stage randomization schemes for Design A of Table 1. (A) Participants are first randomized to Vaccine or Vaccine-placebo, and at the second stage participants willing to be randomized to the NVPM are randomized to NVPM or NVPM-placebo while the remaining participants receive no further intervention. (B) At the second stage, participants desiring to use the NVPM are provided it, participants unwilling to use the NVPM are provided no further intervention, and the remaining participants are randomized to NVPM or NVPM-placebo. Squares denote points of participant decisions and circles indicate points of randomization.