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 alive, it can spread to other parts of the body or to other people from the vaccine site.
For that reason, the vaccine site must be carefully monitored. 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 airborne contagion. The vaccinia virus may cause rash, fever, and head and body aches. Vaccinia is not spread through the air. 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 more serious risks. In the past, about 1, people for every 1 million people vaccinated 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, including eczema vaccinatum, progressive vaccinia or vaccinia necrosum , or postvaccinal encephalitis. 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. People most likely to have side effects are people who have, or even once had, skin conditions, especially eczema or atopic dermatitis and people with weakened immune systems, such as those who have received a transplant, are HIV positive, or are receiving treatment for cancer.
Anyone who falls within these categories, or lives with someone who falls into one of these categories, should NOT get the smallpox vaccine unless they are exposed to the disease.
Pregnant women should not get the vaccine because of the risk it poses to the fetus. Anyone who is allergic to the vaccine or any of its components should not get the vaccine, and anyone under the age of 18 should not get the vaccine unless they are exposed to smallpox. People who should not get the vaccine include anyone who is allergic to the vaccine or any of its components polymyxin B, streptomycin, chlortetracycline, neomycin ; pregnant women; women who are breastfeeding; people who have, or have had, skin conditions especially eczema and atopic dermatitis ; and people with weakened immune systems, such as those who have received a transplant, are HIV positive, are receiving treatment for cancer, are taking medications like steroids that suppress the immune system, or have heart conditions.
Also individuals younger than 12 months of age should not get the vaccine. Additionally, the Advisory Committee on Immunization Practices ACIP advises against non-emergency use of smallpox vaccine in children younger than 18 years of age and the vaccine manufacturer's package insert states that the vaccine is not recommended for use in geriatric populations in non-emergency situations. The term geriatric generally applies to those people age 65 and above. These people should not receive the vaccine unless they have been exposed to smallpox.
Also, people who are using steroid drops in their eyes should wait until they are no longer using the medication to get the vaccine. Careful monitoring of smallpox vaccinations given over recent months has suggested that the vaccine may have caused side effects on the heart. Experts are exploring this more in depth.
As a precaution, if you have been diagnosed by a doctor as having a heart condition with or without symptoms you should NOT get the smallpox vaccine at this time. A second drug, cidofovir, may be used is some situations. Neither drug is currently licensed for this purpose both administered under investigational new drug IND protocol and they may have side effects of their own.
Revisiting historical data is difficult because of incomplete information in a number of areas. These include how many times the subjects were vaccinated revaccination produces longer-lasting immunity , whether the vaccinations were carried out successfully and whether or not subjects ever had a subclinical smallpox infection that would boost their immunity this situation is particularly likely in endemic areas.
The last natural smallpox infection occurred in , so recent advances in immunology and medical testing cannot be brought to bear on this question. Before smallpox was eradicated, the World Health Organization WHO recommended that international travelers to nonendemic countries should be revaccinated every five to 10 years and travelers to endemic countries should be revaccinated every three years.
Lab workers in diagnostic facilities and others more likely to be exposed to the smallpox virus were advised to be vaccinated once a year. The basis for the WHO guidelines was that a history of vaccination within five years was known to offer good protection, whereas the data for vaccination beyond 10 years was difficult to interpret. A conservative estimate of the duration of smallpox immunity was therefore justified. Vaccination 40 years ago, even if not currently protective against smallpox disease, may offer some protection against a fatal outcome.
A study of smallpox cases imported into nonendemic countries found that mortality was 52 percent among the unvaccinated, 11 percent among those vaccinated more than 20 years earlier and 1. Therefore, vaccination 40 years ago most likely does not confer protection against smallpox infection, but it may help to prevent a fatal outcome.
In a public health emergency due to smallpox, the two live vaccines will be used primarily to stop the chain of transmission. Post-exposure vaccination has been shown to be effective because a rapid immune response can be generated in exposed people. The incubation period of smallpox averages 12 to 14 days.
Following vaccination, antibodies can be detected within a week. Observational studies suggest that vaccination within three or four days of exposure may reduce severity of disease. Vaccination four to seven days after exposure may confer some protection. Unlike the two live-attenuated smallpox vaccines, Imvamune was not evaluated during the eradication of smallpox, so its usefulness as post-exposure prophylaxis is unknown.
An Emergency Use Authorization would permit use of this vaccine in children. If vaccination with a live vaccine is successful, a red and itchy bump develops at the vaccination site within three or four days see photos below. The bump becomes a blister, fills with pus and begins to drain. During the second week, the blister begins to dry up and a scab forms.
In the third week, the scab falls off, leaving a small scar. Smallpox vaccines are not available for members of the general public. However, the U. Recommendations for use of the vaccine will be determined by public health authorities based on the characteristics of the outbreak. Animal models of poxvirus infections are being employed to understand what constitutes an effective host response.
Ectromelia virus is closely related to variola virus and it causes a disease similar to smallpox in mice. This model is well established, resistant and susceptible strains of mice are defined and four genetic loci associated with resistance have been identified.
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