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Adverse Reactions

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Expected Reactions link Accidental Administration link Encephalitis link Inadvertent Inoculation link Vaccinia Keratitis link Eczema Vaccinatum link Generalized Vaccinia link Congenital Vaccinia link Progressive Vaccinia link Bacterial Infection link Erythema Multiforme link Adverse Reactions Reference link Adverse Reactions Menu

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Immunity and Adverse Reactions

Immunity to vaccinia is dependent on both cell-mediated immune function and antibody production. In general, individuals with intact cell-mediated immunity do not suffer serious consequences. Individuals with antibody-deficient states but with intact cell-mediated immunity generally handle vaccination without incident. However, there are reports of adverse events, even in this group of vaccinees.

Frequency of Adverse Events

The rates reported in the frequency tables for each adverse event were derived from two studies conducted in the 1960's; one from a 10 state survey and one from a national survey. The actual rates differ in these studies for several reasons; the reports vary in the way in which data were collected, in some instances serious reactions were absent or less frequently reported than in the other study, and the diagnoses were not uniform in definition.

As a result the specific rates may not be as reliable as one would wish. What is apparent is that overall, less serious complications occurred at a rate of 1000 per million vaccinations. Approximately half of these were accidental inoculations occurring most frequently in children. One primary concern is the actual rates for serious adverse events. The national survey data in the tables for each adverse event appear to be more reliable. In initial vaccination programs currently, only adults will be vaccinated and it is difficult to transpose data from either of these studies to expectation of adverse event rates in that population. Data will be collected prospectively to shed light on actual rates in 2002-2003.

Smallpox vaccination (vaccinia) is a generally safe, effective preventative against smallpox.

However, in a number of individuals, smallpox vaccination can result in untoward effects and adverse reactions. Most are totally benign, if frightening in appearance. Some are serious, but treatable. A few, which rarely occur, are serious, life threatening and can be fatal.

All adverse reactions must be reported to the CDC. Please click on the Reporting an Adverse Event button for further information.

Click on any of the adverse reaction images or names at the right to read more about each adverse reaction, including who is susceptible and measures that might be employed to reduce risk to the vaccinee and his/her contacts.


Hospitalization of patients with adverse events should be based on the degree of severity and infectiousness:


Do Not Hospitalize


Non-infectious patients(*)






Severe and
extensive accidental




Post-vaccinial encephalitis()   


* Unless serious disease is present, such as Stevens Johnson Syndrome.
Most patients with generalized vaccinia will not require hospitalization; in fact, it is prudent to avoid hospitalization to minimize intra-hospital spread.
Patients with severe and extensive inoculation vaccinia, progressive vaccinia and post-vaccinial encephalitis almost always require hospital care. In hospital, they must be isolated and care taken to separate all materials used in their care, treating such materials as infectious waste. For further information, please visit the Preventing Contact Transmission page.

Accidental Administration link Inadvertent Inoculation link Bacterial Infection link Congenital Vaccinia link Eczema Vaccinatum link Encephalitis link Erythema Multiforme link Generalized Vaccinia link Normal Primary link Normal Variants link Progressive Vaccinia link Vaccinia Keratitis link Revaccination link All Reactions links