Smallpox is the only human infectious disease we've eradicated. Why?

On May 8, 1980, the World Health Organization declared that smallpox—a highly-deadly disease in humans—had been eradicated. Today it’s still the only one we’ve completely wiped out. So, how’d we do it? And why haven’t we done it for the many other diseases that plague us, like COVID-19? Links to the Tiny Show & Tell stories here and here. Episode transcripts at acs.org/tinymatters   See Privacy Policy at https://art19.com/privacy and California Privacy Notice at https://art19.com/privacy#do-not-sell-my-info.