Mass vaccination programs previously conducted to combat viral epidemics/pandemics (e.g. smallpox, polio, measles, yellow fever) have nothing in common with the ongoing mass vaccination campaigns today as those viruses are very different in ters of their pathogenesis, transmissibility, route of infection, potential reservoirs, predominant effector mechanisms involved in antiviral immunity, susceptibility of population segments, as well as with regard to the vaccines used (all prior vaccination campaigns involved live-attenuated virus).
