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Smallpox

An acute, highly contagious, often fatal infectious disease. Vaccination has succeeded in eradicating smallpox worldwide.

PubMed Health Glossary
(Source: NIH - National Library of Medicine)

About Smallpox

Smallpox, caused by the variola virus, was a highly contagious infectious disease that caused infected individuals to develop a fever and a progressive, disfiguring skin rash. Three of out 10 individuals infected with smallpox died. Many survivors have permanent scars, often on their faces, or were left blind.

Through vaccination, the disease was eradicated in 1980. However, research for effective vaccines, drugs and diagnostics for smallpox continues in the event it is used as a bioterror weapon.

The last naturally occurring case of smallpox was reported in 1977. In 1980, the World Health Organization declared that smallpox had been eradicated. Currently, there is no evidence of naturally occurring smallpox transmission anywhere in the world.

Although a worldwide immunization program eradicated smallpox disease decades ago, small quantities of smallpox virus officially still exist in two research laboratories in Atlanta, Georgia, and in Russia....Read more about Smallpox
NIH - National Institute of Allergy and Infectious Diseases

What works? Research summarized

Evidence reviews

Vaccines for preventing smallpox

Smallpox is an acute viral infection unique to humans. A worldwide smallpox campaign (including mass vaccination, patient isolation, and surveillance) contributed to the eradication of the disease by 1980. However, there is growing concern that the virus could now be used as a biological weapon. Smallpox spreads from one person to another by infected saliva droplets. The incubation period is 7 to 17 days. The symptoms begin with severe headache, backache, and fever up to 40 °C, all beginning abruptly. Then a rash appears on the face and spreads, the spots become watery blisters containing pus that form scabs and leave pitted scars when they fall off. The infected person is contagious until the last smallpox scab has fallen off, although most of the transmission occurs in the first week. Most people with smallpox recover, but some do die and the risk depends on the strain of virus. The early vaccines were effective, but they had a number of adverse effects, including headache, fever, and reaction at the infection site, and also the possibility of death. New vaccines continue to be developed. The review identified 10 trials that involved 2412 participants. Overall, the quality of the trials was not high but the review showed that stockpiles of the vaccines maintained their effectiveness even when diluted. New second‐generation vaccines seemed to be effective but still have adverse events. There were too few participants overall to be able to assess rare outcomes. Further research is needed, particularly on the third‐generation vaccines.

Risks of serious complications and death from smallpox vaccination: a systematic review of the United States experience, 1963 - 1968

This review appeared to conclude that for every million vaccinations there were 60 cases of accidental infection, 40 of generalised vaccinia, 13 of eczema vacciantum, three of post-vaccinial encephalitis and one of vaccinia necrosum. Death rates associated with these complications were reported. The conclusions follow from the evidence presented but the results may not apply to populations vaccinated today.

Respiratory Precautions for Protection from Bioaerosols or Infectious Agents: A Review of the Clinical Effectiveness and Guidelines [Internet]

There are a number of infectious diseases that are transmitted from person to person via the respiratory route, including influenza, tuberculosis (TB), and severe acute respiratory syndrome (SARS) coronavirus, and these infectious agents are associated with considerable morbidity and mortality. Healthcare workers (HCWs) are vulnerable to exposure to these agents given the nature of their jobs, and as a result, risk both becoming infected, and spreading the infectious agents to other patients. To avoid transmission of these infectious diseases to (HCWs), exposure-appropriate respiratory precautions are sometimes necessary to protect both HCWs and the patients they care for. However, the selection of respiratory equipment depends on the pathogen, aerosol generation rate, and ventilation rate.

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Summaries for consumers

Vaccines for preventing smallpox

Smallpox is an acute viral infection unique to humans. A worldwide smallpox campaign (including mass vaccination, patient isolation, and surveillance) contributed to the eradication of the disease by 1980. However, there is growing concern that the virus could now be used as a biological weapon. Smallpox spreads from one person to another by infected saliva droplets. The incubation period is 7 to 17 days. The symptoms begin with severe headache, backache, and fever up to 40 °C, all beginning abruptly. Then a rash appears on the face and spreads, the spots become watery blisters containing pus that form scabs and leave pitted scars when they fall off. The infected person is contagious until the last smallpox scab has fallen off, although most of the transmission occurs in the first week. Most people with smallpox recover, but some do die and the risk depends on the strain of virus. The early vaccines were effective, but they had a number of adverse effects, including headache, fever, and reaction at the infection site, and also the possibility of death. New vaccines continue to be developed. The review identified 10 trials that involved 2412 participants. Overall, the quality of the trials was not high but the review showed that stockpiles of the vaccines maintained their effectiveness even when diluted. New second‐generation vaccines seemed to be effective but still have adverse events. There were too few participants overall to be able to assess rare outcomes. Further research is needed, particularly on the third‐generation vaccines.

More about Smallpox

Photo of an adult woman

Also called: Variola

Other terms to know:
Infectious Disease (Communicable Disease), Viruses

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