The Role of Smallpox in Disaster Preparedness

Vaccination for Variola Hasn’t Been Performed in the US Since 1972

Sep 18, 2009

Two generations of children have reached adulthood in the United States without smallpox vaccinations. As immunity declines, nearly all Americans are susceptible.

Since humans are the only natural host for the smallpox virus, and since the virus cannot survive in the environment for more than two days, the World Health Organization recommended discontinuation of routine smallpox vaccination in 1980. (Smallpox [Variola] in The Merck Manual, 18th Edition. 2006:1647-49)

Laudably, a highly infectious and potentially fatal disease had been eradicated due to global immunization efforts; the smallpox virus was eliminated from the environment.

Unfortunately, the smallpox virus is still stockpiled in high-security laboratories at various locations around the world; deliberate acquisition and dissemination of this biological agent “could cause a public health catastrophe.” (United States Department of Labor: Occupational Safety and Health Administration. Safety and Health Topics: Smallpox. September 3, 2008)

The Effects of Smallpox on Unimmunized Populations

Two strains of smallpox were well-characterized prior to the virus’ eradication (other strains may now exist within containment facilities due to efforts to develop more effective biological weapons). The more virulent native strain caused variola major (classic smallpox), while the less virulent strain caused variola minor (alastrim).

Variola minor begins with a two- to three-day prodrome of headache, backache, fever, and other flu-like symptoms. This is followed by the eruption of a maculopapular rash that starts in the mouth and on the face and arms and quickly spreads to the trunk and arms. The rash then becomes blister-like (similar to chickenpox) and finally progresses to pustules. In 8 – 10 days the rash crusts over, often leaving residual scarring. Mortality in variola minor is less than 1%.

Variola major is similar in presentation and progression to variola minor, but the symptoms and rash are much more severe. Due to a systemic inflammatory response (possibly due to a cytokine storm), shock and multiple organ failure ensue, and 30% of victims die during the second week of the illness.

10% of infected individuals develop a particularly malignant form of variola major – sometimes referred to as hemorrhagic variola – that is almost uniformly fatal within the first week of infection.

Since smallpox is transmitted from person-to-person via direct contact, inhalation of respiratory droplets, or contaminated clothing and linens, and since the “attack rate” among unvaccinated persons approaches 85%, one infected individual can easily infect 10 – 20 others.

The Role of Vaccination in the Event of Smallpox Outbreak

Immunization for smallpox with vaccinia (a less dangerous relative of smallpox) is no longer routine because administration of the vaccine can be accompanied by adverse events, some of which are severe:

Currently, smallpox vaccination is limited to people at high risk for exposure (laboratory technicians who work with the virus, certain healthcare professionals, and military personnel).

It is generally assumed that older individuals who were vaccinated before the eradication of smallpox are once more at risk for smallpox infection, because immunity wanes without continued exposure to smallpox-like viruses (e.g., vaccinia).

In the event of a documented smallpox outbreak, the rapid identification, isolation, and vaccination of contacts of sick persons (and the contacts of their contacts) is of paramount importance. Unfortunately, since smallpox has not been seen by most medical professionals for over 30 years, there will probably be significant delay between the outbreak and its identification.

Even more ominous is the likelihood that anyone deliberately releasing smallpox into a population will do so at more than one location. This will lead to rapid dissemination of a highly-infectious and lethal agent in an immunologically-naïve citizenry.

The Centers for Disease Control and Prevention regularly update disaster preparedness plans and vaccination recommendations for a smallpox outbreak, but it isn’t really clear if stockpiles of vaccines are adequate to stop the spread of contagion.

Although prior planning and education may serve to protect certain segments of society, it is quite clear that smallpox – if reintroduced as an agent of bioterrorism – would quickly overwhelm public health efforts, kill a substantial number of individuals, and paralyze an economy.

The copyright of the article The Role of Smallpox in Disaster Preparedness in Global Security is owned by Stephen Allen Christensen. Permission to republish The Role of Smallpox in Disaster Preparedness in print or online must be granted by the author in writing.