Older people may be immune to swine flu

UNDATED - There are some benefits to being middle-aged. The current strain of the H1N1 virus, commonly known as swine flu, may be similar enough to a strain that spread across the world in 1977 that older people could be immune to it, according to a report from Wired .

The 1977 strain, known at the time as "Russian flu," infected people under 25 at much higher rates than older people, who had been exposed to an earlier strain in the 1940s and 1950s.

Leonard Mermel, an infectious disease specialist at Rhode Island Hospital, wrote, "It might be that the H1N1 circulating now (swine-origin influenza virus) has enough antigenic similarity to related H1N1 influenza strains of the past to protect older individuals exposed to them previously" in a letter to the medical journal The Lancet .

A publication by the Centers for Disease Control lends credence to Mermel's theory. "Results among adults suggest that some degree of preexisting immunity to the novel H1N1 strains exists, especially among adults aged >60 years," CDC scientists wrote in the Mortality and Morbidity Weekly Report .

Larry Madoff, editor of the epidemiological news service, ProMED Mail, said Mermel's hypothesis requires further investigation. "There may be other factors at play here as well," he said. "Kids are together more, confined in schools more. The immunology may not be the whole story."