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Video Transcript: Smallpox Vaccine Administration

Segment 3 of 8:
Adverse Reactions

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Watch this segment of the video RealOne Player RealOne Player format (13 min 20 sec)

Reactions following smallpox vaccination can be divided into three types: local reactions at the site of vaccination; systemic symptoms; and events resulting from transfer or dissemination of vaccinia virus in healthy people or in people with certain underlying medical conditions.

A local reaction at the site of inoculation, like the one shown here, indicates a successful vaccination. But in addition to a pustule, the local reaction at the site of inoculation can be very dramatic.

In several recent studies of old and new vaccines given to unvaccinated adults, the average size of the pustule at 2 weeks after vaccination was 12 millimeters—or about half an inch. The average size of erythema surrounding the pustule was 16 to 24 millimeters, and average induration was 11 to 15 millimeters, or up to 2/3 of an inch.

Some vaccinees may have larger amounts of erythema and induration that can be mistaken for cellulitis. These reactions generally improve within 24 to 48 hours without specific therapy but may require clinical evaluation to rule out bacterial cellulitis.

Forty to 47 percent of the vaccinees reported mild pain at the site of inoculation. But 2 to 3 percent reported the pain as severe. Axillary lymphadenopathy was reported in about one third of recipients. Most lymphadenopathy was mild, but in 3 to 7 percent it was considered moderate—that is, bothersome to the vaccinee but not otherwise interfering with normal activities.

Fever is common after administration of smallpox vaccine. In a recent study of Dryvax given to unvaccinated adults, 5 to 9 percent reported a fever of 100 degrees Fahrenheit or higher, and 3 percent reported temperature of 102 or higher. Fever is most common 7 to 12 days after vaccination. In addition to fever, adult vaccinees also report a variety of constitutional symptoms, including headache, myalgias, chills, nausea, and fatigue on or about the eighth or ninth day after vaccination. One or 2 percent of recipients reported these symptoms as severe.

Historically, fever was more common among children. In past studies, about 70 percent of children experience 1 or more days of temperature of 100 degrees Fahrenheit or higher after primary vaccination. Fifteen to 20 percent of children experienced temperatures higher than 102 degrees Fahrenheit.

Beginning about 4 days after vaccination, vaccinia virus is present at the site of inoculation. If the lesion is touched, virus can be transferred to another part of the body.

Transfer, or autoinoculation, of vaccinia from the vaccination site is called inadvertent autoinoculation. This is the most frequent complication of smallpox vaccination. It usually occurs because the site itches as it heals, and the person scratches the site.

Inadvertent autoinoculation accounted for approximately half of all complications of primary vaccination and revaccination. In studies of smallpox vaccination in 1968, inadvertent autoinoculation occurred at a rate of 25 to 529 cases per million primary vaccinations. Carefully following the site care instructions will significantly decrease the risk of this complication.

Lesions of inadvertent autoinoculation can occur anywhere on the body, but the most common sites usually involved are the face, eyelid, nose, mouth, genitalia, and rectum.

A variety of erythematous and urticarial rashes occur approximately 10 days after primary vaccination. These rashes are referred to as erythema multiforme, roseola vaccinia, toxic erythema, and postvaccinial urticaria.

They are flat, erythematous, macular, or urticarial lesions, usually with microscopic vasculitis. The pathophysiology of these rashes is not well understood. They don't usually become vesicular, and don't appear to involve viral multiplication or systemic dissemination. The rash resolves spontaneously within 2 to 4 days.

Patients with erythematous urticarial rashes associated with vaccinia are generally not severely ill and are usually afebrile despite the sometimes extensive skin involvement. On rare occasions Stevens-Johnson syndrome, or bullous erythema multiforme, may develop.

Another type of rash following smallpox vaccination is called generalized vaccinia. This condition is believed to result from a vaccinia viremia with implantations in the skin in persons without underlying illnesses.

True generalized vaccinia consists of vesicles or pustules appearing on normal skin distant from the vaccination site, and is often accompanied by symptoms such as fever, headache, and myalgias. In the 1968 studies, rashes diagnosed as generalized vaccinia occurred at a rate of 23 to 242 cases per million primary vaccinations.

Most rashes labeled as generalized vaccinia produce only minor illness with little residual damage. The rash is generally self-limited and usually requires no specific therapy.

Three complications of smallpox vaccination are rare, but can be very severe or fatal. These are eczema vaccinatum, progressive vaccinia, and postvaccinial encephalitis.

Eczema vaccinatum is the generalized spread of vaccinia on the skin of a person with eczema or true atopic dermatitis, or a history of eczema or atopic dermatitis. The most serious cases among vaccine recipients occur among primary vaccinees and are independent of the activity of the underlying eczema.

Severe cases have also been observed after contact of a recently vaccinated person with someone who has eczema or atopic dermatitis. It occurred at a rate of 10 to 39 cases per million primary vaccinations.

This person has eczema vaccinatum. This woman had eczema and acquired her infection after contact with her recently vaccinated boyfriend. She survived the illness but had extensive residual scarring of her skin.

Eczema vaccinatum is believed to result from either blood dissemination of vaccinia virus or by direct skin inoculation of vaccinia on skin affected by eczema or atopic dermatitis. Vaccinia virus is readily recoverable from skin lesions. Vaccinia immune globulin or VIG has been shown to be effective for the treatment of this complication.

This person has progressive vaccinia, also known as vaccinia necrosum. Progressive vaccinia is a severe, potentially fatal illness, characterized by a nonhealing vaccination site with progressive necrosis. Metastatic lesions are often present.

Progressive vaccinia occurs almost exclusively among persons with cellular immunodeficiency, but can occur in persons with humoral immunodeficiency. Progressive vaccinia can occur following revaccination of people who have become immunosuppressed since their primary vaccination. In the 1968 studies progressive vaccinia occurred at a rate of 0.9 to 1.5 cases per million primary vaccinations. Progressive vaccinia could be seen more often in today's population, with the greater prevalence of HIV and posttransplant immunosuppression. VIG has variable effectiveness in treating this complication.

A major unpredictable complication is postvaccinial encephalitis. In the majority of cases, postvaccinal encephalitis affects primary vaccinees 12 months of age or younger, and adolescents and adults receiving a primary vaccination. It presents with any of a variety of central nervous system signs, such as ataxia, confusion, paralysis, seizures, or coma. Most cases are believed to result from autoimmune or allergic reactions, similar to other postviral CNS syndromes rather than direct viral invasion of the nervous system.

Approximately 15 to 25 percent of vaccinees with this complication die, and 25 percent develop permanent neurological sequelae. It occurred at a rate of 3 to 12 cases per million primary vaccinations. Treatment of postvaccinial encephalitis is supportive care, as VIG is not effective.

A fetus may be infected if a pregnant woman receives smallpox vaccine. Fetal vaccinia is a rare complication of smallpox vaccination. Fewer than 50 cases of fetal vaccinia infection have been reported. When this complication did occur, it was usually following primary vaccination of the mother in the second or third trimester. Fetal infection following vaccination in the first trimester would presumably result in spontaneous abortion. But studies are contradictory as to whether an increased number of spontaneous abortions actually occurred in pregnant women. Smallpox vaccination of a pregnant woman has not been associated with fetal malformations or birth defects.

Death resulting from smallpox vaccination is rare, with approximately 1 death per million primary vaccinations and 1 death per 4 million revaccinations. Death is most often the result of postvaccinial encephalitis or progressive vaccinia. However, death can also result from eczema vaccinatum.

Vaccinia immune globulin, or VIG, has been used to successfully treat some smallpox vaccine complications. It is a sterile solution of the immunoglobulin fraction of plasma from persons vaccinated with vaccinia vaccine. It's been used to treat eczema vaccinatum, progressive vaccinia, and severe generalized vaccinia.

It's also been used in the treatment of ocular vaccinia resulting from inadvertent autoimplantation. VIG provides no benefit in the treatment of postvaccinial encephalitis or in the treatment of smallpox.

VIG supplies are limited, so it should be reserved for the treatment of vaccine complications with more serious clinical manifestations. CDC is currently the only source of VIG for civilians.

So in summary, reactions following smallpox vaccination, such as fever, erythematous rashes, and autoinoculation are common but generally self-limited. Pain, induration, and erythema at the site of vaccination can be dramatic but are also generally self-limited.

Severe complications, such as eczema vaccinatum, progressive vaccinia, and postvaccinal encephalitis are rare, but can be fatal. Severe complications are more common in persons receiving primary vaccination compared to those being revaccinated. The risk of these rare, severe complications can be reduced by careful medical screening for conditions such as eczema, atopic dermatitis, or immunodeficiency.

More information about smallpox vaccine can be found at

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  • Page last updated December 13, 2002
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