Smallpox

Smallpox is an acute, highly contagious disease caused by the variola virus, which belongs to the orthopoxvirus family. It is characterized by a distinctive progression from prodromal symptoms through a generalized maculopapular rash to fluid-filled pustules with central umbilication, followed by crusting and scarring. Two clinical forms—variola major (severe, ~30% case fatality) and variola minor (milder, <1% fatality)—were recognized, along with modified and malignant variants, particularly in vaccinated or immunocompromised individuals. The disease is exclusively human, with no known animal reservoirs, and its transmission requires close contact between infected individuals.

Early symptoms include high fever, fatigue, headache, backache, nausea, vomiting, and malaise, typically lasting 2–4 days. This is followed by the development of mucosal ulcers and a characteristic rash that begins on the face and extremities and progresses centrifugally. Lesions evolve over several days: macules → papules → vesicles → pustules → crusts, with pustules reaching maximum size by days 6–7 and crusting by days 7–10. Case fatality ranged up to 30% for variola major, especially among infants; survivors often exhibited extensive scarring or blindness. Modified smallpox, seen in previously vaccinated individuals, featured milder symptoms and fewer lesions, while malignant (flat) smallpox presented with non-raising lesions and prolonged viremia, contributing to higher mortality.

Smallpox has existed for at least 3000 years, with historical evidence dating to Egyptian mummies (~1500 BCE). It occurred in recurrent outbreaks across continents, causing millions of deaths before eradication. The global eradication campaign, launched by WHO in 1967, culminated in certification of eradication in 1980 after the last natural case in October 1977 in Somalia. Since then, no naturally acquired cases have been reported. The only post-eradication cases were linked to laboratory accidents, including one fatal incident in Birmingham, England, in 1978. No animal reservoirs or zoonotic transmission are documented.

Transmission occurs primarily through prolonged face-to-face contact with an infected person, via respiratory droplets or aerosols containing virus-laden material. Less commonly, it may be transmitted via contaminated objects (fomites), though this route is considered less efficient. The virus is most infectious during the early febrile phase and when the rash is evolving, with peak infectivity coinciding with the presence of pustules. The incubation period ranges from 7 to 17 days, with an average of 12–14 days. Source-backed detail on environmental persistence or exact duration of infectiousness is not available in the provided snippets.

Historically, unvaccinated individuals—including infants, young children, and those without prior immunization—were at highest risk of severe disease and death. In the context of eradication, risk groups are now largely hypothetical, with the primary concern being individuals exposed to the virus in a laboratory setting or through intentional release. No current population-level risk exists due to the absence of circulating virus.

Prevention was achieved through the smallpox vaccine, first developed by Edward Jenner in 1796 using cowpox material. Vaccination conferred long-lasting immunity and was central to the WHO eradication strategy. Post-exposure vaccination within 3–4 days of exposure could still prevent or attenuate disease. No antiviral treatments were available during the active epidemic era; post-eradication, antivirals such as cidofovir or tecovirimat have been studied but were not deployed during the disease’s natural course. As smallpox is eradicated, routine vaccination is no longer recommended, though stockpiles remain for potential biodefense purposes.

Given the complete absence of natural transmission since 1977 and official eradication status, surveillance for smallpox is not required in routine public health systems. However, any suspected case must be treated as a high-consequence event due to the potential for deliberate release or accidental lab exposure. Surveillance protocols would involve immediate isolation, biosafety containment, and rapid reporting to national authorities and WHO. Risk groups are currently theoretical, as the disease no longer circulates; historical risk groups included unvaccinated individuals, children, and those in endemic regions prior to eradication.

1. 1 WHO Health Topics. Smallpox.
2. 2 WHO Fact Sheet. Detail.
3. 3 WHO Q&A. Smallpox.
4. 4 Wikidata. smallpox.
5. 5 Wikipedia. Smallpox - Wikipedia.

ICD-10

B03

ICD-11

Total cases

0

Peak month

2012-09

Coverage

2 reporting countries · 2012-09-14 → 2026-05-09