Scientists have long thought that smallpox — one of the most devastating diseases to ever afflict humankind — has been around for thousands of years. The World Health Organization, for instance, states that smallpox, caused by the Variola virus, has existed for at least 3,000 years.

However, a new study based on the genetic analysis of the viral DNA obtained from the partially mummified remains of a 17th century Lithuanian child has called this belief into question. The research, published Thursday in the journal Current Biology, reveals that the disease may be just hundreds, rather than thousands, of years old.

“Scientists don't yet fully comprehend where smallpox came from and when it jumped into humans,” senior author of the study Hendrik Poinar, the director of McMaster University’s Ancient DNA Centre, said in a statement released Monday. “This research raises some interesting possibilities about our perception and age of the disease.”

For their research, the scientists extracted a heavily-fragmented smallpox virus DNA from the corpse of a child believed to have died between 1643 and 1665 — a period when smallpox outbreaks were common throughout Europe. When they sequenced the DNA and compared it to the 20th century samples, they found that all available strains of the virus emerged from an ancestor that existed in the 1580s.

“This study sets the clock of smallpox evolution to a much more recent time-scale” study co-author Edward Holmes, an evolutionary biologist from the University of Sydney, said in the statement. “Although it is still unclear what animal is the true reservoir of smallpox virus and when the virus first jumped into humans.”

Tracing the evolutionary history of the deadly pathogen also unearthed a surprising finding — evolution of the virus into a major and a minor strain only began after 1796, when the English physician and scientist Edward Jenner developed a vaccine.

“This raises important questions about how a pathogen diversifies in the face of vaccination,” co-author Ana Duggan, a post doctoral fellow at the McMaster Ancient DNA Centre, said in the statement. “While smallpox was eradicated in human populations, we can't become lazy or apathetic about its evolution — and possible reemergence — until we fully understand its origins.”

The last known case of smallpox was recorded in Somalia in 1977. The virus no longer exists naturally, and all its remaining live stocks are currently being held in two secure laboratories — one in the U.S. and the other in Russia.