The Decline in Smallpox

Deaths from smallpox certainly fell after the introduction of vaccination, but then so did deaths from many other diseases, such as measles and scarlet fever, making it difficult to determine the contribution of vaccination to the fall.
Whilst smallpox vaccination does offer some protection, those opposed to vaccination were persuasively arguing that improvements in sanitation were the true cause of the decline in all these diseases. They also argued that deaths from smallpox were falling despite falling vaccination rates. The accompanying graph shows how the death rate from smallpox was falling despite a fall in the vaccination rate.

Though this graph only shows those children vaccinated at birth, when the large majority were vaccinated, it is not a good advertisement for the effectiveness of smallpox vaccination.1
The number of deaths from smallpox fell sharply during the late nineteenth century and remained low despite falling vaccination figures. As the disease became increasingly rare, and hence the relative risks of vaccination greater, an increasing number of doctors called for the end of vaccination against smallpox.  Compulsory vaccination ended in 1948.

Did vaccination eradicate smallpox?

Mass vaccination had little effect on smallpox. Smallpox disappeared in countries with little or no vaccination, such as Australia and New Zealand, as well as countries with widespread vaccination. Indeed, by the twentieth century, mass vaccination in the UK had been shown to be both ineffective and dangerous. When the World Health Organisation (WHO) launched its Intensified Smallpox Eradication Programme in 1967, its strategy involved mass vaccination of 100% of the populations of countries where smallpox still existed. It soon became clear that this was not working and a different approach was found to be more successful: the ‘surveillance-containment strategy’. This did not rely on mass vaccination but instead depended on quickly finding new cases and isolating them to prevent spread. This was accompanied by selective vaccination of close contacts. This approach proved far more effective than the policy of mass vaccination, and the last case of wild smallpox was diagnosed in Somalia in 1977. Two years later, WHO declared the world free of smallpox.

Would smallpox have disappeared on its own like the Plague?

We will never know.
Mass vaccination alone failed to eradicate smallpox, though it played a part in its elimination, as an accessory to case finding and isolation. Vaccination is not entitled to take all the glory: it was a supporting actor on a stage where the ‘surveillance-containment strategy’ played the leading role. Leading players involved in smallpox eradication have admitted that eradication was a
close shave, and only just achieved.