Smallpox was one of the worst diseases that ever plagued humankind. From the time of the pharaohs until the 20th century, it was a continuous scourge, killing 30 percent of those who were infected, and disfiguring most of the afflicted. The ability to vaccinate against it, and to use vaccine to diminish its spread, culminated in the eradication of smallpox. In 1980, the World Health Organization (WHO) declared that smallpox was no longer causing infections and that vaccinations could cease.
Once smallpox was extinct in the natural world, there were still many scientific questions to address in order to understand how this virus was able to defeat the human immune system so thoroughly. There was also the threat of a new pox virus epidemic. There are many pox viruses in the world, such as monkeypox, which infects humans causing a smallpox-like disease; it was important to understand how different the pox viruses are to estimate their potential to evolve into human threats.
Gronvall, Gigi Kwik. 2015. "Hindsight Not 20/20 for Smallpox Research." START (January). https://www.start.umd.edu/news/hindsight-not-2020-smallpox-research