Despite the development of modern medicine and vaccines, vaccine-preventable childhood infections remain a major burden and even cause of death around the globe. The recent surge in the outbreaks of infectious diseases such as measles and pertussis, together with the severity of the COVID-19 pandemic, have spurred a worldwide search for functional strategies to increase vaccine uptake. This thesis focuses on 18th and 19th century Finland, where before vaccines smallpox was a leading cause of death, killing up to 11% of Finland’s population around 1800. While vaccination against smallpox started in 1802 and eventually eliminated smallpox from Finland in 1941, little is known about how this vaccination campaign was implemented, and to what extent it was successful. In this thesis, I investigated the implementation of Finland’s first vaccination campaign through three key factors: vaccination mandates (Chapter I), socio-economic status (Chapter II), and the family network (Chapter III). To do this, I collected and analysed a series of unique historical records provided by the Finnish National Archives.

First, this thesis showed that mandatory vaccination was successful in improving vaccination coverage by 20% during Finland’s first vaccination campaign, where mean coverage surpassed 80% coverage required for herd immunity against smallpox. However, the law had varied impact on the socio-economic groups. While the >80% coverage of the high socio-economic group was unaffected by the law, the middle socio-economic group saw substantial improvement in coverage after the law. The lowest socio-economic group with initially poor coverage, showed little increase, highlighting the necessity for additional interventions. Though grandmothers improved in child survival from many infectious diseases, including smallpox, they had no effect on vaccine uptake, underscoring the need for alternative strategies to promote vaccination.

These findings enable public health workers to make informed decisions on the strategies to combat declining vaccination coverage. Understanding the success of past vaccination initiatives can help in the management of future outbreaks and offer general conclusions applicable to contemporary vaccination campaigns.