Information about contact transmission from the IHB Clinical Services clinical staff.
Contact Transmission Presentation (pdf)
Clinical Guide to diagnosis and treating contact transmission
Contact Transmission Algorithm (pdf)
Smallpox vaccine contains live vaccinia virus. When a person receives smallpox vaccine, the live vaccinia virus replicates and is shed
at the vaccination site. Unintended transmission of vaccinia virus from a vaccine recipient (vaccinee) to an unvaccinated person (contact)
is known as contact transmission, contact vaccinia, or secondary transmission. Contact transmission results when vaccinia virus spreads from
a vaccination site to another person. Inadvertent transmission can occur as early as two days after vaccination up until the time when the
skin under the vaccination site scab returns to its pre-vaccination state. The lesions that result from contact transmission usually resemble
the vaccinee's smallpox vaccination site. Contacts also may experience minor vaccine-related symptoms, e.g., fever, lymphadenopathy, headache
and body aches. Certain groups of persons who experience contact transmission are at risk for more serious adverse reactions.
The vaccinia virus can be transmitted through direct contact with the vaccination site or fluid from the site, and can also be indirectly
transmitted through contact with fomites (e.g., towels, linen). No data supports vaccinia transmission occurring through aerosolization or
transmission through saliva or seminal fluids. The vaccinia virus cannot be spread once the skin under the vaccination site scab returns to
its pre-vaccination state (i.e., the skin under the scab looks like the skin surrounding the vaccination site.)
The risk of contact transmission is very low if vaccinees and their contacts follow proper vaccination-site care and handwashing technique.
The risk of contact transmission is higher for primary vaccinees than for revaccinees. The risk of serious adverse events from contact transmission
is increased in persons with the following conditions:
The DoD Smallpox Vaccination Program was initiated in December 2002. Between December 2002 and January 2004, the reported rate of contact
transmission was 5 per 100,000. Between February 2004 and May 2009 the reported rate of contact transmission was also 5 per 100,000.
These rates from the current DoD program are similar to overall contact transmission rates during mass immunization programs in the 1950s
and 1960s in the range of 2-6/100,000 vaccinations.
Within DoD-reported contact vaccinia cases, the primary mode of transmission has been through very close contact between the vaccinee and
the contact, with a majority of the contacts described as intimate and the second most common type of contact described as sports-related (e.g., wrestling, basketball).
Reports of serious reactions in cases of contact transmission:
In patients being evaluated for recently appearing lesion(s) compatible with vaccinia infection (e.g., vesicular-pustular lesions):
Possible cases of contact transmission should be reported to the Vaccine Adverse Event Reporting System.
To request clinical consultation and/or to have patient entered in the IHB Clinical Services
Smallpox Contact Transmission Registry, contact the IHB Clinical Services
at 1-866-210-6469 or
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