Transmissible vaccines could help reach populations that are difficult to vaccinate directly or control epidemics. There are two main designs - live attenuated vaccines that create a subdued infection to elicit immunity without disease, and recombinant vector vaccines that combine genomes of a wild virus and benign virus so the benign virus spreads disease antigens. However, both have limitations in transmission and safety risks like genetic reversion or loss of antigens that need to be addressed through collaboration among scientists.