Implements methods for inference on potential waning of vaccine
efficacy and for estimation of vaccine efficacy at a user-specified time
after vaccination based on data from a randomized, double-blind,
placebo-controlled vaccine trial in which participants may be unblinded
and placebo subjects may be crossed over to the study vaccine. The
methods also allow adjustment for possible confounding via inverse
probability weighting through specification of models for the trial
entry process, unblinding mechanisms, and the probability an unblinded
placebo participant accepts study vaccine: Tsiatis, A. A. and Davidian,
M. (2021) .