The existence of the influenza vaccine ... may give us a sense of false security when it comes to the possibility of a pandemic outbreak of influenza. In fact, the flu vaccine must be reformulated each year to keep pace with the newest variants of this fast-mutating virus. The recipe for making the flu vaccine is simple. Take the current year's variant of the influenza virus, throw it into a stew with a strain of virus that leads to rapid proliferation. Incorporate the fast-growing strain into its own genes and start replicating it. From there, it's an easy matter to take those plentiful viruses and attenuate them for a flu vaccine. But the scientists who must determine what virus will cause the next year's illness run a high chance of being wrong. Some observers have put the odds of success at no better than 50-50. Even when they are right, the vaccine lasts only as long as that year's strain. Experts thought they saw big-league trouble coming in February 1976, when a few cases of severe swine flu broke out among young military recruits in Fort Dix, N.J. One of them, Pvt. David Lewis, 19, died. Lewis and four others were shown to be infected with the same H1N1 influenza virus as was responsible for the 1918 pandemic. But the swine-flu pandemic never materialized. In retrospect, some critics now say 40 million Americans were vaccinated for nothing. In fact, the only real illness to result from the swine flu adventure was caused by the vaccine: about one thousand people developed Guillain-Barre syndrome, a serious paralytic disease that could be traced directly to an immunological response to the inoculation.