In the 18th century, smallpox infections swept the globe, terrorizing its victims with the promise of either death or permanent mutilation by scabs. In desperation to escape the disease, people tried numerous preventative actions but experienced almost no success. One popular preventative measure was "variolation" - scratching a person's skin with infectious smallpox virus to give them a rash but not the actual disease. If successful, the person would maybe get a fever but otherwise recover. Then, they would be immune to the more serious, full-on smallpox infection. More often than not, however, people would scratch too deeply, the virus would get into the bloodstream, and the person would be accidentally inoculated with smallpox (NIH).
Fortunately, at the turn of the century, scientist Edward Jenner noticed a connection between smallpox and cowpox, a viral disease of the same family that caused a less lethal disease in humans than smallpox. Jenner noticed that milk maids tending to cowpox-ridden cattle seemed to be immune from smallpox. Smallpox is caused by a viral strain called Variola (CDC). Cowpox, the closely related neighbor, is caused by a viral strain called Vaccinia. Thus, Jenner developed a way to infect people with cowpox to prevent them from ever getting smallpox. He called this preventative inoculation a vaccine.
Recent smallpox studies have focused on examining different Vaccinia strains used in different countries during the 20th century World Health Organization campaign to entirely eliminate the disease. Surprisingly, little was known about the origin of the smallpox vaccine.
Researchers in Brazil from the Universidade Federal do Rio de Janeiro looked at two clones of the vaccine used to eliminate smallpox in Brazil, VACV-1OC. Both clones showed low virulence and and a protective immune response in experimental mice, suggesting both strains would be useful as a "second-generation vaccine" if needed (PUBLICASE COMUNICAÇÃO CIENTÍFICA).
More studies on the genetic history of the smallpox vaccine can be expected to conducted in the future.
Watch the TED-Ed video below to understand more about the eradication of smallpox.
Source: Eurekalert