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The
smallpox vaccine prevents smallpox. For most people, it is safe and effective.
Most people experience normal, typically mild reactions to the vaccine,
which indicate that it is beginning to work. Some people may experience
reactions that may require medical attention.
Normal,
Typically Mild Reactions
These reactions usually go away without treatment:
- The arm
receiving the vaccination may be sore and red where the vaccine was
given.
- The glands
in the armpits may become large and sore.
- The vaccinated
person may run a low fever.
- One out
of 3 people may feel bad enough to miss work, school, or recreational
activity or have trouble sleeping.
Serious
Reactions
In the past, about 1,000 people for every 1 million people vaccinated
for the first time experienced reactions that, while not life-threatening,
were serious. These reactions may require medical attention:
- A vaccinia
rash or outbreak of sores limited to one area. This is an accidental
spreading of the vaccinia virus caused by touching the vaccination site
and then touching another part of the body or another person. It usually
occurs on the genitals or face, including the eyes, where it can damage
sight or lead to blindness. Washing hands with soap and water after
touching the vaccine site will help prevent this (inadvertent inoculation).
- A widespread
vaccinia rash. The virus spreads from the vaccination site through the
blood. Sores break out on parts of the body away from the vaccination
site (generalized vaccinia).
- A toxic
or allergic rash in response to the vaccine that can take various forms
(erythema multiforme).
Life-Threatening
Reactions
Rarely, people have had very bad reactions to the vaccine. In the past,
between 14 and 52 people per 1 million people vaccinated for the first
time experienced potentially life-threatening reactions. These reactions
require immediate medical attention:
- Eczema
vaccinatum. Serious skin rashes caused by widespread infection of the
skin in people with skin conditions such as eczema or atopic dermatitis.
- Progressive
vaccinia (or vaccinia necrosum). Ongoing infection of skin with tissue
destruction frequently leading to death.
- Postvaccinal
encephalitis. Inflammation of the brain.
People with
certain medical conditions—including people with weakened immune
systems or certain skin conditions—are more likely to have these
reactions and should not get the smallpox vaccine unless they have been
exposed to smallpox.
Based on
past experience, it is estimated that between 1 and 2 people out of every
1 million people vaccinated may die as a result of life-threatening reactions
to the vaccine.
A Note on Recent Developments
Data from recent smallpox vaccinations have been found to be consistent with a causal association between vaccination and myopericarditis, although this is not proven. Persons receiving smallpox vaccine should be aware that myopericarditis is a potential complication of smallpox vaccination. If vaccinees experience chest pain, shortness of breath, or other symptoms of cardiac disease after vaccination they should seek medical attention. In addition, heart pain (angina) and heart attack also have been reported following smallpox vaccination, however, it is not known if smallpox vaccination caused these problems or if they occurred by chance alone.
A
Note on Numbers: Most of the statistical information about smallpox
vaccine adverse reactions cited in this fact sheet is based on data from
two studies conducted in 1968. Adverse
event rates
in the United States today may be higher because there may be more people
at risk from immune suppression (from cancer, cancer therapy, organ
transplants,
and illnesses such as HIV/AIDS) and eczema or atopic dermatitis. The
outcome associated with adverse events may be less severe than previously
reported
because of advances in medical care. Rates may be lower for persons previously
vaccinated.
For more about vaccination, see Smallpox
Vaccine.
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Page last reviewed July 30, 2004
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