The panic in 1976 was partly because of the belief — now known to be erroneous — that the 1918-19 flu pandemic, which killed half a million Americans and as many as 50 million worldwide, was caused by a virus with swine components. Recent research suggests instead that it was avian flu, but that seems unlikely to assuage the current anxiety…

At the CDC, Sencer solicited the opinions of infectious disease specialists nationwide and, in March, called on President Ford and Congress to begin a mass inoculation.

The $137-million program began in early October, but within days reports emerged that the vaccine appeared to increase the risk for Guillain-Barre syndrome, a rare neurological condition that causes temporary paralysis but can be fatal.

Waiting in long lines at schools and clinics, more than 40 million Americans — almost 25% of the population — received the swine flu vaccine before the program was halted in December after 10 weeks.