Questions and Answers About Post-event SmallpoxVaccination
If someone is exposed to smallpox, is it too late to get a vaccination?
Vaccination within 3 days of exposure will completely prevent or significantly modify smallpox in the vast majority of people. Vaccination 4 to 7 days after exposure likely offers some protection from disease or may modify the severity of disease.
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. Now, the CDC is recommending that have people have written documentation of vaccination dated within 3 years to be considered protected.
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.
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.
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.
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.
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.
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.
If there were ever a case of smallpox, would pregnant women be vaccinated?
If there is a smallpox outbreak, anyone who is exposed to smallpox should get vaccinated, because they will be at greater risk from the disease than they are from the vaccine. Public health authorities will recommend who should be vaccinated at that time and what measures people can take to protect themselves from smallpox.
If a woman wants to get pregnant, how long does she need to wait after receiving the smallpox vaccine?
A woman should wait until the vaccine site has completely healed and the scab has fallen off before trying to become pregnant after vaccination. Generally, this means women who have received the smallpox vaccine should wait at least four weeks (28 days) before becoming pregnant. 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.
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.
- Page last reviewed: March 13, 2009
- Page last updated: March 13, 2009
- Content source: CDC Emergency Risk Communication Branch (ERCB), Division of Emergency Operations (DEO), National Center for Emerging and Zoonotic Infectious Diseases (NCEZID)
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