Smallpox: 30th Anniversary of Global Eradication

The eradication of smallpox represents one of the greatest accomplishments in modern medicine, science and public health. Today, 30 years after the last patient was diagnosed and treated, we celebrate the hard work and dedication of scores of workers around the world who contributed in the global eradication effort.

Smallpox has always been feared. A serious, contagious, and sometimes fatal infectious disease, it was known to kill up to 30% of its victims and to leave numerous others pitted with scars for life. There was no vaccine or treatment until the end of the 18th century, when Edward Jenner invented smallpox vaccination, and the idea of vaccination itself.

While the disease was largely controlled in Europe and North America by the mid-20th century, it took a concentrated, worldwide effort combining mass vaccination with close surveillance over many years to finally stamp out the disease. The last case of smallpox in the United States was in 1949, and the last naturally occurring case in the world was in Somalia in 1977.

Scientists Look Back to Smallpox Origin

The history of smallpox has been unclear due to significant gaps in historic medical records and competing hypotheses on the origin of the disease. Evidence of smallpox-type rashes can be found on Egyptian mummies dating back to 1100-1580 BC, which supports the idea that the disease was present in Egypt. However, there is no mention of the disease in the Old or New Testaments or in Greek or Roman medical literature.

On the eve of the 30th anniversary of the smallpox eradication, scientists at CDC and the Lawrence Livermore National Laboratory reported on their efforts to look back into time to help unravel the puzzle of smallpox evolution. By analyzing DNA sequences of 47 virus strains from Europe, Africa, Asia, and South America, the team was able to build a “family tree.” They believe that variola virus (the cause of smallpox) had a possible African rodent-borne virus ancestor, from which it diverged, as early as 16,000 to 68,000 years ago. This study, published in the October 2nd issue of the Proceedings of the National Academy of Science (www.pnas.org), indicates that the smallpox may have originated earlier than previously believed.

Smallpox Eradication Timeline

Written descriptions occurred as early as 400 AD.

1796: The first smallpox vaccine was developed by Edward Jenner.

After WWI: Most of Europe smallpox-free.

After WWII: Transmission interrupted in Europe and North America.

1940s: With the development of a freeze-dried vaccine that was more stable in higher temperature and humidity climates, the smallpox vaccine was available for wider use throughout the world.

1950: The Pan American Sanitary Organization, the predecessor to the Pan American Health Organization, undertook a program to eradicate smallpox in the Western Hemisphere.

1958: The first proposal for global eradication was made to the World Health Assembly by the USSR in 1958. They proposed a worldwide vaccination program to be completed in a 3-to-5 year period. Some progress was made during the next 7 years, but the results overall were disappointing.

1966: The World Health Assembly decided to intensify the eradication program by providing a special budget of $2.4 million per year specifically for this effort.

1967: The Intensified Global Eradication program began:

• An estimated 10 - 15 million smallpox cases still occurred in 31 countries where the disease was endemic. More than 1 billion people lived in these areas.

• A major reservoir was Africa, where people in most countries south of the Sahara were infected.

• A second major reservoir was in Asia, extending from Bangladesh through India, Nepal, Pakistan, and Afghanistan.

• The third was the Indonesian archipelago,

• The fourth was Brazil, which compromised half the people of South America.

Global Eradication Initiative

The initial eradication campaign was based on a two-fold strategy.

• Mass vaccination campaigns in each country, using vaccine of ensured potency and stability, that would reach at least 80% of the population.

• The development of surveillance systems to find cases and outbreaks so that more focused containment measures could be implemented.

 Mass Vaccination

In 1966, the Smallpox Eradication and Measles Control Program was initiated in 18 West African countries to move toward eradication in this disease-endemic area. At that time, Sierra Leone had the highest infection rates in the world.

Through the use of vaccination guns, government resources, and, most importantly, traditional health authorities, large numbers of people were vaccinated. The program administered over 100 million vaccinations in a 5-year period. Surveys showed that 90% of the population had been vaccinated. Smallpox rates fell as a result of these efforts.

The program had to overcome numerous problems, including lack of organization in national health services; epidemic smallpox among refugees fleeing areas stricken by civil war and famine; shortages of funds and vaccine; and a host of other problems posed by difficult terrain, climate, and cultural beliefs.

Surveillance and Containment

It was possible to have an great impact on smallpox transmission even in areas where overall vaccination coverage was low by using a strategy called surveillance and containment, or ring vaccination. This strategy became the key strategy in the global eradication program.

The principle behind this strategy was to

• identify cases of smallpox,

• vaccinate their household and other close contacts, and then

• vaccinate the close contacts of the primary household and close contacts to the case.

If the primary contacts developed smallpox despite vaccination, their close contacts would already be protected and the chain of transmission would have been broken.

Special surveillance teams were recruited and trained to search for smallpox cases and vaccinate their contacts. They visited each health unit in an area of endemic smallpox to ensure that each week the health officer submitted a report indicating the number of cases seen. When cases were reported, the teams worked with local health staff to find additional cases and to contain the outbreaks by vaccinating the contacts.

Although setbacks occurred, this surveillance and containment strategy proved to be the strategy that finally brought about the eradication of smallpox throughout the world.

Final Eradication

By the end of 1975, smallpox persisted only in the Horn of Africa.

Conditions were very difficult in Ethiopia and Somalia, where there were few roads. Civil war, famine, and refugees made the task even more difficult. With the interruption of smallpox transmission in Asia, more resources were made available in Africa, including more staff and transport.

An even more intensive surveillance and containment and vaccination program was initiated in the spring and summer of 1977. As a result, the world’s last indigenous patient with smallpox on earth was a hospital cook in Merka, Somalia, on October 26, 1977 with variola minor.

Searches for additional cases continued in Africa for more than 2 years, during which time thousands of rash illnesses were investigated. None proved to be smallpox.

Although 2 cases of smallpox occurred in England in 1978 as a result of a laboratory accident, smallpox was gone as a naturally transmitted disease.

The World Health Organization officially certified that smallpox had been eradicated on December 9, 1979, 2 years after the last case in Somalia. In 1980 the World Health Assembly recommended that all countries cease routine vaccination.

This global effort rid the world of a deadly disease that had plagued humankind for centuries. It is thanks to the work of scores of individuals, and the tremendous worldwide cooperation, that future generations will likely know of smallpox only through historical references.

For more information:

• Smallpox Information

• Smallpox Vaccination: Information for Health Professionals

• The History of Bioterrorism: Smallpox