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Can Smallpox and Monkeypox (Mpox) cause injury and/or death?

Updated November 03, 2023


Yes, before smallpox was declared eradicated in May 1980 by the World Health Organization (WHO) the virus was circulating in the environment and caused serious illness and often death.

Symptoms of Variola Major, the most common form of smallpox illness, included: 

  • Anorexia
  • Vomiting
  • Malaise
  • High fever (between 101°F to 105°F)
  • Chills
  • Headache
  • Backache
  • Severe abdominal pain
  • Pharyngitis
  • Extreme exhaustion
  • Rash, more frequently seen in light-skinned individuals

When the fever resolved, rash lesions would begin to develop and appear in the back of the mouth, behind the oral cavity (oropharynx), followed by the face, arms, legs, and then would spread to the torso, and palms and soles. Rash lesions developed evenly during the illness and progressed from macules to papules to vesicles within 4 to 5 days. In another one or two days, the vesicles evolved to pustules that were round, firm, and found deep in the dermis. Crusting and scabbing of the lesions usually began on the ninth day and the crusts generally began to fall off about 2 weeks after the onset of the rash. 

Complications of smallpox included severe bacterial infections of the skin and organs, sepsis, pneumonia, encephalitis, and keratitis. 

The most common long-term health consequence of smallpox was scarring which could occur all over the body but most often on the face. Additional sequelae included stillbirths and spontaneous abortions, infertility in males, osteomyelitis, encephalitis, and blindness. Persons who recovered from smallpox illness developed long-term immunity.  Historically, Variola Major was fatal in approximately 30 percent of cases. 

Malignant (Flat-type) Smallpox, a rare form of smallpox that was more common among children, was identified by skin lesions that developed slowly, merged together, and would become soft and flat. Most cases of flat-type smallpox were fatal due to toxemia, however, if a patient survived, the rash would heal without scabbing.  This type of smallpox was fatal in approximately 97 percent of cases. 

Hemorrhagic smallpox, a form of smallpox similar to Variola Major, had a shorter incubation period and prodromal symptoms that were usually more severe. Additionally, after the onset of illness, skin redness would occur and progress to a petechial rash (small pinpoint purple or red rash) and hemorrhaging of the skin and mucous membranes. Hemorrhagic smallpox was usually fatal by the fifth or sixth day after rash onset, and frequently as a result of multi-system organ failure due to toxemia.  Nearly all cases of hemorrhagic smallpox were fatal. 

Persons who developed modified smallpox, a form of the disease that occurred in smallpox vaccinated individuals when the vaccine failed to protect, would frequently suffer from fever, severe headache, backache and would have a rash lasting as long as a typical illness. The rash, however, would generally evolve through its stages more quickly and lesions were more superficial.  Modified-type smallpox infections were rarely fatal. 

Monkeypox (Mpox)

Symptoms of mpox are similar to smallpox but generally milder. Individuals infected with mpox usually present with headache, backache, fever, chills, muscle aches, extreme fatigue and exhaustion. Swelling of the lymph nodes also occurs, which is a symptom not present with smallpox infection. 

Complications of mpox illness include sepsis, encephalitis, eye infections that may result in blindness, bronchopneumonia, and other secondary infections.  

Three clades (types) of mpox that have been identified: Clade I, Clade IIa and Clade IIb.  Clade I, which is found in the Congo Basin of Africa, is more easily transmissible and associated with higher rates of mortality. Historically, those most at risk have been individuals hunt, kill, and eat bushmeat.  Fatality rates from Clade I mpox are estimated at 10 percent. 

Clade IIa is typically found in West Africa and is rarely fatal, with a mortality rate of less than one percent. Clade IIb is the strain associated with the 2022 global outbreak, and is rarely fatal in immunocompetent individuals. Unlike Clade I and Clade IIa, which generally spreads from animals to humans, Clade IIb is easily transmitted from human to human. 

IMPORTANT NOTE: NVIC encourages you to become fully informed about smallpox/monkeypox (Mpox) and the smallpox/monkeypox (Mpox) vaccine by reading all sections in the Table of Contents, which contain many links and resources such as the manufacturer product information inserts, and to speak with one or more trusted health care professionals before making a vaccination decision for yourself. This information is for educational purposes only and is not intended as medical advice.

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