The swine flu virus may have enough similarity to the previously circulated H1N1 strains or those used in past vaccines, according to a Rhode Island Hospital expert. Hence it may lead to protection of older individuals.
Leonard Mermel, an infectious diseases specialist at the hospital, has identified characteristics of the outbreak of H1N1 in 1977 and speculated its impact on the current pandemic in a letter to the editor, published in the journal the Lancet.
Mermel notes that in the late 1970s, an influenza H1N1 reappeared in humans. It had a pandemic-like spread that began in younger aged individuals.
He points out that the strain, known as the "Russian flu" H1N1, was similar to H1N1 strains that circulated internationally between 1946 and 1957.
The expert further writes in the letter that the Russian flu spread rapidly across the former Soviet Union, initially affecting individuals between the ages of 14 and 20 in schools, as well as young military personnel, and later spread to preschool children.
Individuals older than age 30, however, had dramatically lower attack rates and the overall mortality was low. The epidemic peaked rapidly, with a relatively short duration.
According to the letter, the first outbreak of the Russian flu in the US occurred in a Wyoming high school. The attack rate there was over 70 percent, but it affected students only and no faculty were reported to have the illness.
High attack rates were seen in schools as well as military bases throughout the US, similar to the outbreak in Russia. There were few reports of the H1N1 strain in individuals older than age 26, and again, the mortality rate was low.
In his commentary, Mermel hypothesizes that older population may have had enough exposure to past H1N1 flu strains to avoid infection.