Post-Exposure Vaccination
Epidemiological evidence indicates that vaccination within 3 days of exposure to smallpox will prevent or significantly modify smallpox in the vast majority of persons. Vaccination from 4-7 days will also likely modify the severity of the disease and protect against a fatal outcome.
Vaccine Availability
In the event of a smallpox attack, vaccine in amounts sufficient
to immunize the entire population of the U.S. if needed is available.
The lyophilized Dryvax calf-lymph vaccine was prepared in the 1970’s,
but has recently been tested for viability and re-licensed. It has
also been shown to still be potent at a 1/5 dilution. Therefore,
the licensed vaccine could be diluted and used under an Investigational
New Drug Protocol to provide 5 times as many doses if needed during
a smallpox emergency.
A similar calf-lymph vaccine preparation produced by Aventis-Pasteur in the 1950's has also been tested recently and found to be fully potent. It is available as a liquid virus suspension in a glycerinated diluent (not lyophilized). It is stored in 100 dose vials. If needed, this vaccine can also be diluted under an emergency use protocol to provide additional vaccine doses. The technique of administration is exactly as described on the Vaccination Method page for the other vaccines.
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Emergency Vaccination Strategy
If smallpox occurs, priority will be given to:
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Early diagnosis of cases |
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Vaccination of all those who had been in contact with the patient since onset of fever |
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Vaccination of all household members of the contacts |
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Vaccination of healthcare workers, public health personnel,
first responders, and other personnel who will be assisting
with outbreak control measure and emergency response activities. |
This is called surveillance and containment; some call it "ring vaccination".
The ring vaccination has two functions: 1) provide protection to people who were in contact with smallpox virus, and 2) form a barrier of immunity around them by vaccinating their close contacts. Even if the vaccine is given too late for this primary protection and the initial contact develops smallpox, vaccination of his household contacts will serve to provide a barrier of immunity to prevent further spread.
The strategy was successfully employed in the eradication effort. It is based on the fact that infected individuals do not transmit infection until they become ill. Preceding the rash is a prodrome marked by severe systemic illness with high fever. Most patients are too ill to move about during this period and stay in bed. Thus, most secondary transmission occurs either in the home or in the hospital where the person has sought care. Should the number of cases warrant it, community-wide voluntary vaccination can be used to supplement the surveillance-containment strategy.
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