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Dermatologic Adverse Events

Contact Transmission (Smallpox Vaccine)

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.

Routes of Transmission

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:

  • Dermatologic disorders: If persons experience contact transmission and have a history of atopic dermatitis (eczema) or have other skin conditions that disrupt the epidermis, there is a small risk for the occurrence of a rare, but serious, complication called Eczema vaccinatum (EV). EV is a potentially fatal illness that occurs in the skin of patients with atopic dermatitis (eczema) and in other skin conditions in which there is an altered skin barrier. The skin becomes widely infected with vaccinia. The estimated risk of EV during smallpox vaccination programs in the 1950s and 1960s was 1-2 cases/100,000 vaccinations.
  • Compromised Immune Status: If persons who are immunosuppressed due to HIV infection, autoimmune conditions, malignancy, radiation treatment, medications, or immunodeficiencies experience contact transmission, there is a small risk of a rare, but very serious complication called Progressive Vaccinia (PV), or a condition called Generalized Vaccinia (GV) occurring.
    • Progressive Vaccinia (PV) is characterized by painless progressive necrosis at the vaccination site with or without metastases to distant sites. The estimated risk of PV based on adolescent and adult smallpox vaccinations from 1968 studies in vaccinees was 2-35 cases/1,000,000 vaccinations.
    • Generalized Vaccinia (GV) is a disseminated vesicular or pustular rash that is usually benign and self-limited among immunocompetent hosts. The skin lesions of GV are thought to contain virus spread through the blood stream. The estimated risk based on historical reports is 66 cases/million vaccinations.
  • Pregnancy: Fetuses of pregnant women who experience contact transmission are at risk for a rare complication called fetal vaccinia. Fetal vaccinia occurs when the vaccinia virus infects the unborn baby and is manifested by skin lesions and organ involvement, often resulting in fetal or neonatal death. This complication is so rare that according to CDC there have only been 50 cases ever reported in the world.
  • Infants: The risk of serious complications from vaccinia transmission from adult vaccinees to infants aged <1 year is higher than the risk of serious adverse events among older children and adults. This risk is related to the infant's developmental immaturity and behavioral characteristics that could lead to inadvertent exposure.

Smallpox Vaccination Experience, December 2002 - May 2009: Contact Vaccinia

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:

  • There have been no reported cases of contact transmission of vaccinia from healthcare workers to patients.
  • Eczema Vaccinatum: There has been one case of eczema vaccinatum involving contact transmission reported.
  • Progressive Vaccinia: There have been no cases of progressive vaccinia involving contact transmission reported.
  • Fetal Vaccinia: There have been no cases of fetal vaccinia among pregnancies followed by the Smallpox Vaccine in Pregnancy Registry as of Nov 2009. The Smallpox Vaccine in Pregnancy Registry, established in 2003 and managed by the Department of Defense Birth and Infant Health Registry, follows women who inadvertently received the smallpox vaccine or experienced contact transmission while pregnant. 


In patients being evaluated for recently appearing lesion(s) compatible with vaccinia infection (e.g., vesicular-pustular lesions):

  • Ask about close contact with Smallpox vaccinees.
  • If there is a clear history of close contact with a smallpox vaccinee, a high degree of suspicion for contact transmission should be raised.
  • If a history of close contact with a smallpox vaccine is not clear, other viral etiologies that can be confused with vaccinia infection (i.e., varicella, herpes zoster, herpes simplex, and enteroviruses) should be considered.
  • Contacts should be assessed for the presence of conditions that may increase their risk of serious complications secondary to contact transmission.
  • Obtain lab specimens to identify infectious agent. If PCR positive, record as medically immune in vaccination records.
  • PCR (polymerase chain reaction assay for vaccinia) is available through military or state regional laboratories participating in the Emergency Response Lab Network. If unable to obtain prompt local support for PCR and culture, contact the Immunization Healthcare Division by email or telephone. After hours, call the Worldwide DHA Immunization Healthcare Support Center at (877) GET-VACC or (877) 438-8222.
  • Information on obtaining viral PCR and culture specimens: Available on the CDC website.


To decrease the risk of contact transmission in high risk populations, screening efforts should exempt people who have household or intimate contacts with weakened immune systems, are pregnant, or have exfoliative skin conditions. One of the most critical measures in preventing contact transmission is hand hygiene after any contact with the vaccination site or contact with materials that have come into contact with the site. Vaccinees should keep their vaccination sites covered. Recommended dressings include nonstick bandages, semi-permeable dressings, and dry gauze. The dressing should be changed daily or every few days (according to type of bandaging and amount of exudate). To reduce contact transmission risk further, wearing long-sleeve clothing is recommended and should be worn when close contact with others is anticipated. Vaccination dressings should be properly disposed of. Dispose of bandages and materials in contact with the vaccination site or fluids from the vaccination site in sealed or double plastic bags. Bleach, alcohol, or soap may be carefully added to kill the virus. 


Support CenterPossible 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 IHD Clinical Services Smallpox Contact Transmission Registry, contact the Worldwide DHA Immunization Healthcare Support Center at 1-877-438-8222, Option 1.


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CDC. Vulvar vaccinia infection after sexual contact with a military smallpox vaccinee--Alaska, 2006. MMWR Morb Mortal Wkly Rep. May 4 2007;56(17):417-419.

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Savona MR, Cruz WP, Thornton JA, Danaher PJ. Comparison of a semipermeable dressing bonded to an absorbent pad and a semipermeable dressing over a separate gauze pad for containment of vaccinia virus at the vaccination site. Infect Control Hosp Epidemiol. Dec 2007;28(12):1339-1343.

Stark JH, Frey SE, Blum PS, Monath TP. Lack of transmission of vaccinia virus. Emerg Infect Dis. Apr 2006;12(4):698-700.

Talbot TR, Peters J, Yan L, Wright PF, Edwards KM. Optimal bandaging of smallpox vaccination sites to decrease the potential for secondary vaccinia transmission without impairing lesion healing. Infect Control Hosp Epidemiol. Nov 2006;27(11):1184-1192.

Vora S, Damon I, Fulginiti V, Weber SG, Kahana M, et al. Severe eczema vaccinatum in a household contact of a smallpox vaccine. Clin Infect Dis. 2008 May 15; 46(10):1555-61.

Lewis FS, Norton SA, Bradshaw RD, Lapa J, Grabenstein JD. Analysis of cases reported as generalized vaccinia during the US military smallpox vaccination program, December 2002 to December 2004. J Am Acad Dermatol. 2006 Jul;55(1):23-31. 

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Last Updated: August 24, 2022
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