Post-Exposure
Vaccination
Epidemiological evidence indicates that vaccination within
2-3 days after exposure to smallpox can result in protection
against the disease and, even as late as 4 to 5 days, may protect
against a fatal outcome.
Vaccine
Availability
In the event of a smallpox attack prior to the availability of
tissue cell-culture vaccine, sufficient amounts of calf-lymph
vaccine are available from CDC. The calf-lymph vaccine (Dryvax/Wyeth)
was prepared and lyophilized in the 1970’s, but has recently
been tested for viability and found to be potent at a 1/5 dilution.
It is stored in 500 dose vials.
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 virus suspension in a glycerinated
diluent. It is stored in 100 dose vials. The technique of administration
is exactly as described for the tissue cell culture vaccine
on the Vaccination Method page.
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Emergency
Vaccination Strategy
If smallpox occurs, priority will be given to
• Early diagnosis of cases
• All those who had been in contact with the
patient since onset of fever
• All household members of the contacts
This is called surveillance and containment; some call it "ring
vaccination."
The ring vaccination has two functions. Even if the vaccine
is given too late for this primary protection and the 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 the infected individual does not
transmit infection until he first develops a rash. 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. Should the number of
cases warrant it, community-wide vaccination may be used to
supplement the surveillance-containment strategy.
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