Flu pandemics are followed by recurrent outbreaks for around two decades

Influenza pandemics cause a persistent increase in influenza mortality risk, lasting around two decades, according to new research analysing historical data from the 19th and 20th centuries. The latest study - which is led by researchers at the University of Glasgow, and including academics at Lancaster University - reveals new and important findings about the persistent health impacts of flu pandemics beyond the main waves of infection. In particular, the research found that the main influenza pandemic waves were always followed by multiple sizeable flu outbreaks, in some cases doubling the death toll of the pandemic over the following decade. In addition, the study also found that for almost two decades after an influenza pandemic there remained a high risk that any flu outbreak could cause as many as a third of the deaths of the main wave. Studying data from eight large cities in the UK during the ten years following the 1918-19 global flu pandemic, the researchers were able to show that multiple recurrent influenza outbreaks from 1920-29 resulted in nearly as many deaths as the main waves. It was a pattern they were able to confirm using data for the same period in the US, alongside further data for multiple influenza pandemics during the period 1838-2000 in England and Wales. Taking a closer look at the deaths caused by influenza at both a country and city level in the UK, the research team were able to demonstrate the increased death toll from flu lasted almost two decades after a pandemic initially hit.