Skip directly to search Skip directly to A to Z list Skip directly to navigation Skip directly to site content Skip directly to page options
CDC Home

Questions and Answers About Pre-event Smallpox Vaccination

Why the restriction of smallpox vaccination to persons less than 65 years of age (and greater than 18 years)?
At this time the vaccine is not recommended for the general public. The original restriction was based on absence of studies about smallpox vaccination in the "geriatric" age group, which CDC defined as 65 years and greater. This cutoff was chosen for simplicity. However, if an individual older than 65 is asked to participate in a smallpox response team (and does not have a contraindication to receiving the vaccine,, they can volunteer and be vaccinated. At this time, vaccination against smallpox is only recommended for laboratorians who work with orthopox viruses, and public health and health care response team members. It is unlikely that smallpox response team members are under the age of 18, but can be older than 65.

Will Level A and B Laboratory staff be required to get vaccinated?
No. Level A and B laboratory staff will not be required to be vaccinated, but vaccination will be offered through the Laboratory Response Network. Generally, however, the amount of virus in specimens for routine clinical laboratory testing, and not virus diagnostic testing, would be low and good laboratory safety practices should protect laboratory staff from exposure. For more information on laboratory safety practices, please see the "Biosafety" section of the Public Health Emergency Preparedness and Response Laboratory Information page at

Is there any need for people who have been vaccinated for smallpox as children to be vaccinated?
Yes. Smallpox vaccination provides high level immunity for 3 to 5 years and decreasing immunity thereafter. Someone who was vaccinated decades ago may retain some immunity but it is not known for certain that this level of immunity would protect them from smallpox. They must have written documentation of vaccination dated within 3 years.

What about studies which indicate that immunity following smallpox vaccination may last many years? Do these findings warrant a change in smallpox recommendations?
Recent studies of immunity to smallpox after vaccination have found that people vaccinated many years ago still have measurable levels of antibodies against the disease. While these findings are interesting, they do not provide sound evidence for altering smallpox vaccination recommendations. There is still much about the duration of immunity following smallpox vaccination that we do not know. First, when smallpox disease existed, studies were not done to determine what levels of antibody were protective against exposure to the disease. While antibody may still be present in people who were vaccinated many years ago, it is not known if those antibody levels are high enough to provide protection against smallpox. Second, antibody production is not the only way the immune system responds to antigens. The immune system also remembers, identifies, and destroys invading bacteria and viruses, like the smallpox virus, through what is called "cell-mediated immunity." Cell mediated immunity involves responses including the activation of macrophages and NK-cells and the production of white blood cells called T lymphocytes. The level and duration of cell-mediated immunity following smallpox vaccination is unknown. Finally, data collected while smallpox was still endemic in certain parts of the world show that while some protection against death may last many years after vaccination, many people who had been previously vaccinated still got sick and died from smallpox (and spread the disease to others). In one study of a smallpox outbreak in Europe, the rate of death in people who had been vaccinated 20 years or more before was 11% (the rate in unvaccinated people was 41%). Smallpox response team members would be at high risk of exposure to the smallpox virus if an outbreak were to occur. For their safety, any response team member who has not been vaccinated in the past three years should get the vaccine.

Should pregnant women receive the smallpox vaccine?
No; not if there are no cases of smallpox. In a pre-event situation, women who are pregnant or planning to become pregnant within 4 weeks after vaccination should NOT get the smallpox vaccine. In addition, anyone who has a close contact who is pregnant should not get the vaccine (close contacts include anyone living in your household and anyone you have close, physical contact with such as a sex partner or someone with whom you share a bed). The smallpox vaccine is a live viral vaccine that is made from a virus called vaccinia. Live virus vaccines are generally not recommended during pregnancy. Pregnant women should not get the smallpox vaccine unless they have been in contact with someone with smallpox disease. The vaccine can cause a very rare but serious complication in the fetus called fetal vaccinia (less than 50 cases of fetal vaccinia have ever occurred). However, most babies born after smallpox vaccine exposure will be fine. If a woman is vaccinated she should prevent pregnancy for a month. She should wait until the vaccination site has completely healed and the scab has fallen off before trying to become pregnant after vaccination. Until that time, effective measures should be taken to prevent pregnancy, such as birth control pills, injections, implants, IUDs, or abstinence. Other methods of birth control, such as condoms, diaphragms, spermicide, and natural family planning are less effective.

Should a woman of child-bearing age get a pregnancy test before receiving a smallpox vaccine?
Any woman who thinks she could be pregnant should perform a pregnancy test, by using her first morning urine, on the day vaccination is scheduled. However, even the most sensitive tests may not be able to detect early pregnancies (those less than two weeks along). Thus, if a woman thinks she might be pregnant, she should not get the smallpox vaccine in a pre-event situation.

Is an inadvertently inoculated person considered immune?
Yes, an inadvertently inoculated person who develops a "take-like" reaction at the inoculation site should be considered immune.

If a person responds to a smallpox vaccine with a generalized vaccinia, does this provide them with lifetime immunity to smallpox?
If no, when is another smallpox vaccine contraindicated? Generalized vaccinia is the result of the systemic spread of virus from the vaccination site. Despite the appearance of the lesions, it is a totally benign complication of primary vaccination. Its frequency is not known but it is believed to be rare. There is no lifetime immunity from the vaccine. Past experience indicates that the first dose of the vaccine offers high level protection from smallpox for 3 to 5 years, with decreasing immunity thereafter. If a person is vaccinated again later, immunity lasts longer.

Is there a way to assay immune titers in humans post vaccination?
If so, how long after immunization with vaccinia does the immune titer continue to rise? Previous exposure to smallpox or smallpox vaccine has been historically detected by neutralization antibody test, haemagglutinin-inhibiting antibody tests and complement fixation tests of the person's serum. Neutralizing antibodies develop on average 10 days after primary vaccination and 7 days after revaccination. The levels of antibody reported by these test indicate only exposure, and the protective antibody titer against smallpox infection is unknown. Smallpox vaccination provides high level immunity for 3 to 5 years with decreasing levels thereafter with the antibody persisting for more than 10 years. Someone who was vaccinated decades ago may retain some immunity but it is not known for certain that this level of immunity would protect them from smallpox.

On the Pre-Event Screening Worksheet, there is a question about food allergies. Why is this included on the form? Are food allergies a contraindication?
Food allergies themselves are not a contraindication to smallpox vaccination. However, atopic dermatitis (often called "eczema") is a contraindication, whether or not it is currently active and regardless of severity. There are other types of eczema that do not contraindicate if they are healed, but people with skin conditions often are unable to say whether the conditions are atopic dermatitis or another type of eczema. The questions on the Pre-Event Screening Worksheet are meant to help individuals determine if they, or their close contacts, are likely to have eczema or atopic dermatitis and should not be vaccinated. A diagnosis of food allergies as a child, in combination with having asthma or hay fever, is an indicator that an individual's skin condition may have been atopic dermatitis, and they should not receive the smallpox vaccine. People with atopic dermatitis are frequently misdiagnosed as children or babies as having food allergies.

I am allergic to eggs. Can I still get vaccinated against smallpox?
An egg allergy is not a contraindication to smallpox vaccination. Egg is not used in the manufacture of the vaccine.

What should I do if my vaccination site doesn’t heal in the normal 14-21 days?
Several factors can contribute to the speed of healing of the site, including the type of dressing, the vigor of the take, and the occurrence of secondary infection at the vaccination site. If you have any concerns about your vaccination site you should contact the clinic where you received the vaccine.

Can pets be vaccinated? If so, will they transmit vaccinia to humans?
During the smallpox era, the only known reservoir for the variola virus was humans. Consequently, there was not a need to vaccinate animals (including domestic pets) to protect them from smallpox. If the question is, "Can vaccinia be transmitted to an animal from a human with an unhealed vaccination site?" The answer is Yes. Should an animal develop an active vaccinia lesion, then it should be possible to transmit vaccinia virus from that animal to another human. The best protection is to avoid exposing domestic pets to unhealed vaccination sites or to fomites contaminated with fluid from a vaccination site. These are recommendations to avoid human to pet transmission: Do not let animals sniff or have direct contact with the vaccination site or the bandages, clothing, sheets, etc that have been direct contact with the scab --Keep pets out of the room when you are changing bandages or changing clothes --Before allowing your pet back in the room after you have changed your bandage, place the bandage in a sealable plastic bag before disposal into the trash. Put any clothing that had contact with your scab in the laundry and wash your hands well after touching the site or dressing --Make sure that pets and other animals do not have access to trash containers that have bandages in them.

Is it safe for pregnant women to have contact with a person who has recently received the smallpox vaccine?
Women who are pregnant should not have close contact with anyone who has recently (within the last 28 days) received the smallpox vaccine. A close contact includes anyone living in your household and anyone with whom you have close, physical contact (such as a sex partner or someone you share a bed with). Other friends or people you work with are not considered close contacts.

Where can I get information about the military's smallpox vaccination program?
Information is located on the Department of Defense (DoD) Smallpox Vaccination Program Web site at Questions can be emailed directly to:; or call 1-877-GET-VACC (1-877-438-8222) TOLL FREE; 703-681-5101 DSN 761; Fax 703-681-4692; 8am EST - 6pm EST, Monday - Friday (except Federal holidays).

Contact Us: - Prepare. Plan. Stay Informed. The U.S. Government's Official Web PortalDepartment of Health and Human Services
Centers for Disease Control and Prevention   1600 Clifton Rd. Atlanta, GA 30333, USA
800-CDC-INFO (800-232-4636) TTY: (888) 232-6348 - Contact CDC-INFO

A-Z Index

  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #