Smallpox Vaccine

What is the smallpox vaccine?

The smallpox vaccine is the only way to prevent smallpox. The vaccine is made from a virus called vaccinia, which is another “pox”-type virus related to smallpox.

The vaccine helps the body develop immunity to smallpox. It was successfully used to eradicate smallpox from the human population.

Is the vaccine still given?

Routine vaccination of the American public against smallpox stopped in 1972 after the disease was eradicated in the United States. Until recently, the United States government provided the smallpox vaccine only to a few hundred scientists and medical professionals who work with smallpox and similar viruses in a research setting.

After the events of September and October, 2001, however, the government took further actions to improve its level of preparedness against terrorism. For smallpox, this included updating a response plan and ordering enough smallpox vaccine to immunize the American public in the event of a smallpox outbreak. The vaccine is not available to the public at this time.

How is the smallpox vaccine given?

The smallpox vaccine is not given with a hypodermic needle. It is not a “shot,” like many vaccinations. The vaccine is given using a bifurcated (two-pronged) needle that is dipped into the vaccine solution. When removed, the needle retains a droplet of the vaccine. The needle is then used to quickly prick the skin 15 times in a few seconds. The pricking is not deep, but it will cause a sore spot and one or two drops of blood to form.

The vaccine usually is given in the upper arm.

If the vaccination is successful the following will occur at the site of the vacccination:

  • A red and itchy bump develops at the vaccination site in three or four days.
  • In the first week after vaccination, the bump becomes a large blister, fills with pus, and begins to drain.
  • During week two, the blister begins to dry up and a scab forms.
  • The scab falls off in the third week, leaving a small scar.

People who are being vaccinated for the first time may have a stronger “take” (a successful reaction) than those who are being revaccinated.

Many vaccines are required. Why don’t people have to get the smallpox vaccine?

The last case of smallpox in the United States was in 1949. The last naturally occurring case in the world was in Somalia in 1977. After the disease was eliminated from the world, routine vaccination against smallpox among the general public was stopped because it was no longer necessary for prevention.

How long does the vaccination last?

Past experience indicates that the first dose of the vaccine offers protection from smallpox for three to five years, with decreasing immunity thereafter. If a person has been revaccinated the immunity lasts longer.

If someone is exposed to smallpox, is it too late to get a vaccination?

Vaccination within three days of exposure will completely prevent or significantly modify smallpox in the vast majority of persons. Vaccination four to seven days after exposure likely offers some protection from disease or may modify the severity of the disease.

Are diluted doses of smallpox vaccine as effective?

Recent tests have indicated that diluted (i.e., watered-down) smallpox vaccine is just as effective in providing immunity as full-strenth vaccine.

Is it possible for people to get smallpox from the vaccination?

No. The smallpox vaccine does not contain smallpox virus and cannot spread or cause smallpox. However the vaccine does contain another virus called vaccinia, which is “live” in the vaccine.

Because the virus is live, it can spread to other parts of the body or to other people from the vaccine site. This can be prevented through proper care of the vaccination site (e.g., handwashing and careful disposal of used bandages). For that reason, the vaccine site must be cared for carefully.

What are the symptoms of vaccinia?

The vaccinia virus may cause rash, fever, and head and body aches.

How is vaccinia spread?

Vaccinia is spread by touching a vaccination site before it has healed or by touching bandages or clothing that have become contaminated with live virus from the vaccination site. Vaccinia is not spread through the air.

How safe is the smallpox vaccine?

The smallpox vaccine is the best protection you can get if you are exposed to the smallpox virus. Most people experience normal, usually mild reactions that include a sore arm, fever, and body aches. In recent tests, one in three people felt bad enough to miss work, school, or recreational activity or had trouble sleeping after receiving the vaccine.

However, the vaccine does have some risks. 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 include a vigorous (toxic or allergic) reaction at the site of the vaccination and spread of the vaccinia virus (the live virus in the smallpox vaccine) to other parts of the body and to other people. These reactions typically do not require medical attention.

Rarely, people have had very bad reactions to the vaccine. In the past, between 14 and 52 people per 1 million vaccinated experienced potentially life-threatening reactions. Based on past experience, it is estimated that between 1 and 2 people out of every 1 million people vaccinated will die as a result of life-threatening reactions to the vaccine.

Careful screening of potential vaccine recipients is essential to ensure that those at increased risk do not receive the vaccine.

Is there a treatment for bad reactions to the vaccine?

Two treatments may help people who have certain serious reactions to the smallpox vaccine. These are Vaccinia Immune Globulin (VIG) and cidofovir.

Since December 2002 the CDC has stockpiled more than 2,700 treatment doses of VIG (enough for predicted reactions with more than 27 million people vaccinated), and 3,500 doses of cidofovir (enough for predicted reactions with 15 million people vaccinated).

Additonal doses of VIG are being produced, and measures are underway to increase supplies of cidofovir. VIG and cidofovir are both administered under investigational new drug (IND) protocol.

Who should not get the vaccine?

Persons who have ever been diagnosed with eczema or atopic dermatitis should not be vaccinated, even if the condition is not currently active. Additionally, persons with household contacts that have a history of these skin conditions should not be vaccinated.

People who have other acute, chronic or exfoliative skin conditions (e.g., burns, impetigo, chicken pox, contact dermatitis, shingles, herpes, severe acne, or psoriasis) or current surgical incisions should not be vaccinated until the condition resolves.

The vaccine should not be given to people with weakened immune systems such as those who have received a transplant, are HIV positive, are receiving treatment for cancer, or are taking medications (like topical or inhaled steroids) that suppress the immune system, or women who are pregnant. These contraindications also apply to anyone who has household contacts with these conditions.

The following additional contraindications apply only to people who may get the vaccine and not their household contacts:

  • Anyone who has had a previous allergic reaction to the smallpox vaccine or any of the vaccine’s component should not receive the vaccine.
  • The vaccine should be deferred in anyone who is moderately or severely ill until the condition has resolved and anyone who is under the age of 18, breastfeeding or has eye diseases of the conjunctiva should not receive the vaccine.

These conditions are subject to update by the Centers for Disease Control and Prevention. If a person in one of these categories is exposed to the smallpox virus it is recommended that they receive the vaccine.

Source: Centers for Disease Control and Prevention.

Contact Information

(702) 759-1671

Updated on:  January 11, 2019