Volunteers needed to test new smallpox vaccine | Science Blog:
No people will be exposed to smallpox as a part of LC16m8 clinical studies. Montoya explained that while it would be valuable to know whether the vaccine is effective against smallpox, for obvious reasons the tests of effectiveness must be done in animals. A study published in May 2004 demonstrated that LC16m8 provided complete protection against poxvirus-an animal virus similar to smallpox-infection in both rabbits and mice. Future studies will be required to confirm the vaccine candidate's efficacy.
Why do we think the animal models will tell us about the effects on humans? Because all mammals have a common ancestors, our responses to similar molecules is similar. That assumes common descent and makes testable evolutionary hypotheses.