Old folks vs. swine flu
Older people may be more immune to the swine flu than everyone else.
The protection theory, Dr. Jernigan explained, is that from 1918 to 1957, all circulating seasonal type-A flus were weakened descendants of the 1918 Spanish flu, which was an H1N1, as the current swine is. […] Then in 1957, an H2N2, the Asian flu, emerged and displaced it. It was replaced in 1968 by the H3N2, called Hong Kong flu, which has persisted as a seasonal strain. A different and milder H1N1 emerged in 1977. It was isolated in China but is called the Russian flu because of a suspicion it escaped from a Soviet laboratory. That H1N1, the 1968 H3N2 and a B strain have all circulated in humans ever since, and the seasonal flu shot is aimed at them.
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