### A Bayesian framework for the ratio of two Poisson rates in the context of vaccine efficacy trials∗

In many applications, we assume that two random observations x and y are generated according to independent Poisson distributions $\left(\lambda S\right)$𝒫(λS) and $\left(\mu T\right)$𝒫(μT) and we are interested in performing statistical inference on the ratio φ = λ / μ of the two incidence rates. In vaccine efficacy trials, x and y are typically the numbers of cases in the vaccine and the control groups respectively, φ is called the relative risk...