Vaccination of animals against disease protects them from suffering. However, this comes with an animal welfare cost - the safety and efficacy of vaccines is assessed in experimental animals and the tests involved can cause significant pain and distress. There is an ethical dilemma in protecting one set of animals at the expense of others but implementation of the 3Rs can help to resolve this. The research animals department works with researchers involved in vaccine testing and regulators to promote the 3Rs in this important area.