When using platform technologies such as ChAdOx1 or DNA or mRNA vaccines, rather than starting from the pathogen itself, there is no risk of failing to inactivate the pathogen being vaccinated against (as with the polio vaccine in 1955) or to weaken it sufficiently. The platform technologies increasingly in use in the 2020s are either not live at all, or live but replication-deficient, meaning they can therefore never spread through the body and cause infection and disease.
