Writing in the journal Lancet, Leonard Mermel of Rhode Island Hospital speculates that much of the world’s older population carries immunity due to exposure to the “Russian flu,” which swept around the world during the late 1970s similarly to the current swine flu virus.

Those born after that time were not exposed to the Russian flu, and are more likely to suffer infection in the current pandemic, according to the article.

Mermel writes that a similar pattern was noted among flu victims in the late 1970s.

The Russian flu was similar to H1N1 strains that spread around the world between 1946 and 1957.

Adults exposed to those strains had a relative immunity to the Russian flu decades later.

Photo: U.S. Centers for Disease Control and Prevention