Share of total deaths due to smallpox by age during the Great Pandemic of 1870-1875

Depending on the reach and level of vaccination within Europe's various states in the 1870s, smallpox had a varied impact on various age groups. For infants below the age of one year, smallpox was responsible for between 15 and 30 percent of all deaths in the given regions, as many of these babies had not yet been vaccinated and were at a high risk of succumbing to the virus. In states where the vaccination of infants was not compulsory, such as the Netherlands, Berlin (Prussia) and Leipzig (Saxony), the share of deaths due to smallpox among young children remained high, while it was relatively low in Hesse and Scotland, who had introduced mandatory vaccination in 1815 and 1864 respectively.

Great Pandemic highlights the need for revaccination

As Hesse had been vaccinating on a large scale for generations, the share of smallpox deaths was relatively low among young people; however, between 1870 and 1872, over half of all deaths among those aged 30 to 60 years were due to smallpox. The reason for this was because smallpox vaccination in infancy did not guarantee lifelong protection, therefore immunity often wore off in adulthood. In the 1830s and 1840s, several German armies started to vaccinate new recruits regardless of whether they had been vaccinated in infancy or not; when scientists compared the smallpox death rates in the army with that of the civilian population during this pandemic, they noticed that it was much lower in the army, due to these revaccination policies. This discovery helped many scientists in Europe recognize the need for revaccination, which greatly contributed to the eradication of the disease across most of Europe in the early twentieth century.