Smallpox has been around since the dawn of recorded history; there are even Egyptian mummies with pockmarked faces, Adalja said.
"It was a big scourge of the human race until it was eradicated from the planet in 1980," Adalja told Live Science.
The first vaccine against smallpox was developed in the 1700s, when biologist Edward Jenner noticed that women who milked cows were immune to smallpox after they had been infected with the much milder disease of cowpox, or vaccinia. So in 1796, Jenner inoculated people using pus from those infected with the cowpox virus, creating the world's first vaccine.
For hundreds of years, the live vaccinia vaccine was grown in cow skins, then in tissue cultures in the lab, but such vaccines caused complications. Scientists have since developed a third-generation vaccine that uses live-but-weakened virus, and doesn't have those side effects, said Grant McFadden, a virologist at the University of Florida who studies poxviruses.
Thanks to a worldwide effort to wipe out the disease, smallpox was declared officially eradicated in 1980, after the last natural occurrence of the disease happened in Somalia in 1977, and the last death from the disease occurred due to a laboratory accident in England in 1978, according to the World Health Organization.