A world free of smallpox for 30 years

On 9 December 1979, a group of eminent scientists announced that the smallpox virus had been eradicated in nature, a statement endorsed by the World Health Assembly the following year.

Smallpox is an acute contagious disease caused by the variola virus, a member of the orthopoxvirus family.

In 1967, when the World Health Organization launched its plan to eradicate smallpox, the disease threatened 60 per cent of the world’s population, killing every fourth victim, and there was no form of treatment.

The global campaign was a startling success, and the last natural case was in Somalia in 1977.

Immunisation was stopped in the UK in 1974 and, in 1979, WHO recommended that vaccination against smallpox be stopped in all countries, the exception being special groups such as researchers in facilities dealing with the smallpox virus.

Smallpox vaccine contains live vaccinia, a virus closely related to variola. It is prepared from pulp scraped from vaccinia-infected animal skin, with phenol added at a concentration sufficient to kill bacteria but not to inactivate the vaccinia virus.

The vaccine is then freeze-dried and sealed in ampoules for later resuspension in sterile buffer. In 1998 approximately 90 million doses of smallpox vaccine were available worldwide.

The seed virus used to produce the vaccine is held at the WHO Collaborating Centre in the Netherlands, where the vaccines are tested for potency every five years. Vaccines stored for almost 20 years have been shown not to have lost their potency.

When Edward Jenner developed the vaccine in 1798, he believed that it imparted lifelong immunity. However, it has been shown that immunity wanes with time, with high levels of protection remaining for 10 years after vaccination, although some studies have found some degree of protection against smallpox for as long as 30 years after vaccination.

From experiences in Europe in the early 19th century it is known that when vaccinated persons contract the disease, the illness is considerably milder than that seen in those who are not vaccinated, and the mortality rate is lower. These patients are also less infectious and are less likely to spread the disease to close contacts.

The fact that many of today’s adults were vaccinated as children could have a significant effect on the dynamics of a smallpox outbreak today, for example, at the hands of bio-terrorists.