ABSTRACT
INTRODUCTION Numerous human diseases still require the development of efficacious and innocuous vaccines. Many of the vaccines developed for human use are based on live attenuated pathogens (polio, yellow fever, measles, mumps, rubella). They result in a limited infection that reproduces mildly the pathogenesis of the disease followed by complete recovery and allow for a full protection upon subsequent contraction of the pathogen. They are still used today against some diseases, and next generations of live attenuated vaccines are being developed that are as efficacious and safer for the individual as the environment.
