Reports indicate that the route of admin-istration of challenge virus and vaccine affects the magnitude ofneutralizing antibodies [94]. In addition, protection from systemicor localized disease requires different antibody targets [95] mak-ing this an important aspect of surrogate model design. As humanstudies of vaccination must rely on challenges that utilize non-systemic infections (i.e. challenge with vaccines), surrogate modelsthat exhibit systemic infection are important.The data gaps identified in this review for both epidemi-ological reports from the eradication era and more modernsurrogate studies indicate a need for additional studies in sur-rogate models. Although it has been challenging to implementthe FDA animal rule for product review [96], the regulatory andscientific communities have made significant progress in clarify-ing what is needed to provide the appropriate data for use inregulatory product review [12]. The three models identified pre-viously in this review as most advantageous for post-exposurevaccination studies (MPXV-macaque (intratracheal microsprayaerosol), MPXV-CAST/EiJ mouse (intranasal), and MPXV-prairie dog(intranasal)) meet many of the requirements for surrogate mod-els. Each of these use a human pathogen as a challenge virus,routes/doses of vaccine that are similar to those tested in humanvaccination trials and routes of challenge that approximate res-piratory infection in humans. Lastly, the macaque and prairiedog models offer a disease presentation that most closely mimicshuman infection, the prairie dog and mouse models are relativelycost-effective and the mouse and macaque models have the bestavailability of immunological reagents for determining the corre-lates of protection in post-exposure vaccination studies. Therefore,a combination of post-exposure studies using all three of thesemodels offers our best chance of not only understanding post-exposure vaccination efficacy but also successfully testing newvaccines against OPXV infection in a post-exposure setting.The question of the efficacy of post-exposure vaccination againstsmallpox is not a trivial one. “Sound administrative procedure mustdepend on accurate knowledge of epidemiology; once the latteris defined the former becomes clear” [31]. While the historicalhuman data from the eradication era is and has been indisputablyimportant, it represents smallpox vaccination with 1st generationvaccines in a global population where immunosuppression by HIVinfection and medical treatments were relatively low. Withoutmodern epidemiologic information on human cases of smallpox intoday’s population using newer vaccines, policymakers are design-ing medical countermeasures against OPXVs in the absence ofhuman infection data. To make informed decisions, research mustcontinue to bridge the gaps between historic smallpox epidemiol-ogy and laboratory research. This can only be accomplished throughthe wise use of current surrogate models and the development ofimproved models.