It was in May 1980 that the World Health Assembly declared the world free of naturally occurring smallpox.
By Michelle Roberts
BBC News health reporter
Since then, there has not been a single case.
Had eradication not been achieved, the past 25 years could have seen some 300 million new victims and an estimated 100 million deaths.
But how did doctors stamp out the "speckled monster".
Smallpox is caused by the variola virus.
This comes in two strains: the less severe variola minor and the more deadly variola major.
It is highly infectious, and has an incubation period of between seven and 17 days.
Then symptoms such as headache, delirium and vomiting emerge, followed the development of the trademark rash.
It kills approximately one in three of those infected.
The virus has been around for centuries. The mummy of Egyptian king Ramses V, who died in 1157BC, was found to bear a rash which resembled that of smallpox.
In 1519AD, the ships of Hernan Cortes landed in Mexico, carrying with them the smallpox virus. More than three million people died when a series of epidemics erupted, finally toppling the centuries-old Aztec Empire.
Back in the 10th century in China and India, a process called variolation was developed.
The total cost of eradication was US$300 million
It took over 200,000 staff in over 70 countries to carry out the work
The total number of doses of vaccine used came to 2,400 million
Source: World Health Organization
This involved taking pus from the pocks of someone suffering from smallpox and inoculating healthy people with it to give lifelong immunity.
Usually a mild case of smallpox developed, but in up to 2% of cases the person died.
Another big disadvantage was that variolated people could pass on severe smallpox to others.
The real breakthrough in fighting the virus came in 1796, when Edward Jenner carried out his famous experiment.
Rulers killed by smallpox
King Ramses V of Egypt (pictured)
Queen Mary II of England
Emperor Joseph I of Austria
King Luis I of Spain
Tsar Peter II of Russia
Queen Ulrika Elenora of Sweden
King Louis XV of France
Source: World Health Organization
He inserted pus extracted from a cowpox pustule on the hand of a milkmaid, into an incision on the arm of an eight-year-old boy, James Phipps.
Jenner proved his theory, drawn from the folklore of the countryside, that milkmaids who suffered the mild disease of cowpox never contracted smallpox.
By 1801, more than 100,000 people had been vaccinated in England.
But it was not until one hundred years later that Jenner's vaccination vision was finally realised.
In 1959 the World Health Assembly passed a resolution to undertake the global eradication of smallpox.
At this time there were still 50 million cases of smallpox every year.
It was thought that by vaccinating or revaccinating 80% of the population within a four to five year period, smallpox could be banished from endemic areas.
However, many countries did not have the funds or the manpower to do this.
Even when the vaccination rate was achieved, smallpox often persisted.
By 1967, vaccination had reduced the number of smallpox to about 10-15 million. WHO decided more action was needed and launched an intensified plan to stamp out the virus for good.
Seek and destroy
Four endemic areas were identified - Africa, Asia, Indonesia and Brazil.
It was decided that more emphasis needed to be placed on surveillance.
Even in areas where vaccination coverage was poor, smallpox spread could be stopped quickly by identifying and isolating patients with the infection and vaccinating their contacts.
Special surveillance teams, made up of the local community and international volunteers, were recruited and trained. These visited public places such as schools and the even remotest areas.
Brazil's last case was detected in 1971 after a huge programme of mass vaccination and case searching, which included the Amazon basin.
India, Pakistan and Bangladesh, with a population of more than 700 million people, presented a special problem. Surveillance-containment measures proved far less effective in these densely populated areas.
In 1973, health authorities decided the only way forward was to conduct a house-by-house search for cases of infection.
In heavily infected areas this was done each month and in less infected areas every second or third month.
As the numbers found began to decrease, a reward for the detection of a case was offered to the first person reporting it and to the health care worker investigating it.
It took only two years for this strategy to work.
After successful eradication in Asia in 1975, the focus shifted to the Horn of Africa - the last foothold of the disease in the world.
The last known natural case of smallpox occurred in 1977 in Somalia in a 23-year-old hospital cook who made a full recovery.
Since then, the only known cases were caused by a laboratory accident in 1978 in Birmingham, UK, which killed one person and caused a limited disease outbreak.
In 1979 it was agreed that all remaining stocks of the virus would be destroyed or passed to one of two secure laboratories - one in the US and one in the Russian Federation.
Since then, no other laboratory has officially had access to the virus.