COVID-19 has been the worst pandemic since the ‘Spanish flu’ of 1918-19, to which it has often been compared at the national and global level. We analysed a long time series of deaths from infectious and non-communicable diseases using detailed archival records for the City of Glasgow to construct a rich dataset of causes of mortality from 1898 to 1972. The archival records confirm that, for Glasgow, the 1918-19 influenza pandemic was the most significant outbreak since the start of the 20th century, that led to an increase in all-cause mortality that, until June 2020, exceeded that of COVID-19. They also demonstrate that the 1918-19 pandemic was followed by a period of heightened volatility in death rates from influenza and related diseases, reflecting more frequent outbreaks, before settling into a regime of smaller fluctuations post-1940. Hence, experience from 1918-19 suggests the potential for a fairly extended period of frequent outbreaks following a pandemic, at least at local scale.