On December 9, 1979, a commission of scientists declared that
smallpox had been eradicated. The disease, which carries around
a 30 percent chance of death for those who contract it, is the only infectious disease afflicting humans that has officially been
eradicated.    
    
Recent research indicates that the smallpox virus may have evolved
as late as 1580 CE.

Dr. Donald A. Henderson (1928-2016) was the epidemiologist
who led the international war on smallpox that resulted
in its eradication.

A self-described “disease detective,” Dr. Henderson being
vaccinated for smallpox.