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The threat of terrorism has raised the spectre of the use of biological agents as weapons. One of the possible agents is the variola virus, the cause of smallpox.

On October 26, 1977, Ali Maow Maalin came down with smallpox in the town of Merka in Somalia. Within a few weeks he was fully recovered. Since that time, not a case of smallpox (except as a result of one laboratory accident) has been discovered anywhere in the world. By May of 1980, the World Health Organization (WHO) felt that it could confidently announce that smallpox had been completely eradicated.

The WHO also asked that all countries with any stocks of variola virus in their laboratories either

Although 74 countries did so, the fear remains that some countries may have retained stocks of the virus.

Even before the complete eradication of smallpox, routine vaccination against the disease was halted in most Western countries. So today anyone under 30 years of age is fully susceptible and even those older may have lost protection against the disease.

A Little History

Smallpox certainly qualified as one of the greatest scourges of humanity. It regularly killed 25% and sometimes as many as 50% of its victims. How was such a pestilence eradicated? Four factors were decisive.
  1. The variola virus, which causes the disease, attacks only humans; no animal reservoirs have been found (as they have for the yellow fever virus, the rabies virus, and the plague bacillus).
  2. If the victim recovers, the virus is completely eliminated from the body. There are no smallpox "carriers" as there are for such diseases as typhoid fever and malaria.
  3. An effective vaccine was available. The vaccine could quickly establish a strong (and reasonably long-lasting) immunity. Thus the chain of contagion could be quickly broken by vaccinating all possible contacts associated with a new case.
  4. The WHO and the countries involved provided personnel, money, and the determination to do the job. An effective vaccine had, as we shall see, been available since 1796 and had already rendered many parts of the world free of the disease during the first half of the 20th century. But still the disease smoldered in Asia, Indonesia, Brazil, and Africa. Only a heroic public health effort — a campaign that began in 1967 — finally eliminated it worldwide.


The first effective attempts to cope with smallpox were made in some of the same regions — Asia, India, Africa — that were the last to be freed of the disease.

The technique was deliberately to inoculate susceptible individuals (i.e., those with no pockmarks to indicate that they had survived an earlier epidemic) with material taken from the pustules of people with a mild case of the disease. This practice, called variolation, induced an active case in the recipient, but usually the case was less severe than if the disease had been contracted in the normal way (by inhalation as it turned out).

Variolation was introduced into England and the American colonies early in the 18th century. The practice was often accompanied by violent controversy.

Nonetheless, the practice gradually gained favor until it was replaced by vaccination. This table (from J. B. Blake, Public Health in the Town of Boston, 1630-1832. Harvard University Press, 1959) shows the effect of variolation on the death rate from smallpox during three epidemics in Boston.

Year 1721 1764 1792
Population 10,700 15,500 19,300
Natural Smallpox
Cases 5,759 699 232
Deaths 842 124 69
Deaths/1000 cases 146 177 298
Smallpox Caused by Variolation
Cases 130 4,977 9,152
Deaths 2 46 179
Deaths/1000 cases 15 9 20


Edward Jenner was a Gloucestershire physician who introduced the practice that led to the elimination of smallpox. Jenner's success was grounded on two observations:
  1. The observation that farmers who had ever contracted cowpox would not contract smallpox. Cowpox is a disease that produces pustules on the teats and udders of cows. Persons in close contact with cows frequently contracted the disease and suffered a mild and transient infection.
  2. The inability to variolate successfully those who had an earlier case of cowpox.
Jenner systematically exploited these observations. Jenner's procedure, which we call vaccination, (L. vacca, cow) quickly replaced variolation as a public health measure because: Jenner's was the first safe and successful attempt to artificially induce an active immunity. Many successful attempts have followed since Jenner's day, but the principles that guided him are still followed:

Because of Jenner's success, the term vaccine is used today for all such preparations. The administration of a vaccine is called immunization.

Link to page describing the various vaccines now in use and their success in reducing disease.

The viruses used in today's smallpox vaccines are called vaccinia viruses. They may be descendents of cowpox or, more likely, the related horsepox virus.

What's Next?

Jenner himself was so confident of the efficacy of vaccination that he wrote:
"the annihilation of smallpox must be the final result of this practice".

In 1980, his prediction seemed to have been fulfilled. Today we are not so confident.

What should we do now?

The argument against universal vaccination is that present vaccines are not 100% safe. There is a small, but definite, risk of serious complications from the vaccine itself, especially in people who have an immunodeficiency (e.g., from AIDS or taking immunosuppressant drugs).

Such problems can be avoided by

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2 February 2018