Researchers at the University of Arizona have solved the mystery surrounding the 1918 pandemic flu virus. The new study uncovered answers regarding the origin of the pandemic as well as its unusual severity.

Michael Worobey, University of Arizona researcher and professor in the UA Department of Ecology and Evolutionary Biology, and his team found that previous flu exposure during childhood may be the key to understanding flu pandemics.

Worobey’s paper regarding the flu was published in Proceedings of the National Academy of Sciences on April 28. The paper provides information about the 1918 pandemic and indicated that the flu viruses people were exposed to during childhood might predict how susceptible they are to future strains. This information could help with vaccination strategies as well as pandemic prevention and preparation.

In a statement, Worobey said, “Ever since the great flu pandemic of 1918, it has been a mystery where that virus came from and why it was so severe, and in particular, why it killed young adults in the prime of life.” He continued, “It has been a huge question what the ingredients for that calamity were, and whether we should expect the same thing to happen tomorrow, or whether there was something special about that situation.”

The researchers developed a molecular clock approach, which they then used to reconstruct the origins of the 1918 pandemic H1N1 influenza A virus (IAV), the classic swine H1N1 influenza virus and the seasonal variant of H1N1 that occurred seasonally from 1918 to 1957. The researchers did not find any evidence to support existing theories about the origins of the 1918 virus, such as the fact that it was transmitted directly from birds or that it resulted from genetic swapping between human and swine influenza strains.