Older Adults May Have Some Immunity to...( CDC says the strain is related to flu...),Health

CDC says the strain is related to flu variant that circulated before 1957

WEDNESDAY, May 20 (HealthDay News) -- Some older people may have partial immunity to the new H1N1 swine flu virus because of possible exposure to another H1N1 flu strain circulating prior to 1957, a U.S. infectious-disease expert said Wednesday.

"The further back you go in time, the more likely you are to have been exposed to H1N1 virus back before 1957, and there is a possibility that having exposure to that virus many years ago may allow you to have some [antibody] reaction to the new H1N1 that's now circulating," Dr. Daniel Jernigan, deputy director of CDC's Influenza Division, said during a teleconference.

That may explain why the new swine flu outbreak is striking a disproportionately large number of children and young adults. The regular seasonal flu typically takes the biggest toll among the very young and the elderly.

The current H1N1 virus is a distant genetic cousin of the more virulent H1N1 "Spanish flu" virus of 1918 that killed 20 million to 50 million people worldwide, and up to 500,000 in the United states. Seasonal versions of this virus circulated throughout the United States until it was replaced in 1957 by the H2N2 "Asian flu" pandemic virus, which caused 70,000 deaths in the United States.

In 1977, the H1N1 "Russian flu" virus emerged, but people exposed to H1N1 before 1957 were largely immune to this strain, according to the U.S. National Institute of Allergy and Infectious Diseases.

Jernigan said studies have found evidence of H1N1 antibody activity in blood from older people. "We can infer from that, to some degree, that there is some level of protection," he said.

But he added a note of caution, saying that many years have passed and the new virus, although the same subtype, is different from the H1N1 seasonal flu virus circulating before 1957.

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