In the United States, a limited reserve supply of vaccine that was produced by Wyeth Laboratories, Lancaster, Pa, in the 1970s is in storage. This supply is believed to be sufficient to vaccinate between 6 and 7 million persons.
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A clandestine aerosol release of smallpox, even if it infected only 50 to 100 persons to produce the first generation of cases, would rapidly spread in a now highly susceptible population, expanding by a factor of 10 to 20 times or more with each generation of cases.2, 10, 38 Between the time of an aerosol release of smallpox virus and diagnosis of the first cases, an interval as long as 2 weeks or more is apt to occur because of the average incubation period of 12 to 14 days and the lapse of several additional days before a rash was sufficiently distinct to suggest the diagnosis of smallpox. By that time, there would be no risk of further environmental exposure from the original aerosol release because the virus is fully inactivated within 2 days.
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In the event of an aerosol release of smallpox and a subsequent outbreak, the rationale for vaccinating patients suspected to have smallpox at this time is to ensure that some with a mistaken diagnosis are not placed at risk of acquiring smallpox. Vaccination administered within the first few days after exposure and perhaps as late as 4 days may prevent or significantly ameliorate subsequent illness.39 An emergency vaccination program is also indicated that would include all health care workers at clinics or hospitals that might receive patients; all other essential disaster response personnel, such as police, firefighters, transit workers, public health staff, and emergency management staff; and mortuary staff who might have to handle bodies. The working group recommends that all such personnel for whom vaccination is not contraindicated should be vaccinated immediately irrespective of prior vaccination status.
Vaccination administered within 4 days of first exposure has been shown to offer some protection against acquiring infection and significant protection against a fatal outcome.15 Those who have been vaccinated at some time in the past will normally exhibit an accelerated immune response. Thus, it would be prudent, when possible, to assign those who had been previously vaccinated to duties involving close patient contact.
That article's from 1999. Since then, post-9/11, more stocks of vaccine have been found, and later trials have shown that the vaccines from the '70s could still be effective if diluted 10:1. At least that's the official line; it's possible they're blowing sunshine up our skirts.