In this regular column, Club Vita’s longevity experts will help you visualise the often abstract world of longevity risk by introducing some of their favourite charts.
In this edition, James Freeman considers whether excess winter deaths are affected by specific flu strains.
Question:
Are excess winter deaths affected by specific flu strains?
Answer:
As ever, it’s difficult to separate causation and correlation, but recent winters with heavy mortality have coincided with higher prevalence of the H3N2 strain of flu.
The chart below, which featured in our recent VitaMins Health bulletin on the effects of flu, shows the number of deaths in England & Wales each quarter from 2010 to mid-2019. The blue bars represent winter deaths, showing a spike in deaths in the first quarter of each year. We have overlaid the flu subtypes which were most prevalent each year (by number of identified cases).
Key considerations
- Recent years of heavy winter mortality corresponded with a higher prevalence of the H3N2 strain of flu.
- This suggests that H3N2 may have been a more life-threatening strain of flu in recent years.
Other factors also effect the severity of winter mortality. Cold weather, poorly insulated homes and the price of fuel all mean that cold homes are also a major cause of excess winter deaths. The effectiveness of the flu vaccine also contributes to how severely the population is hit by the particular wave of seasonal flu.
However, H3N2 causes so many more problems for health practitioners than other strains that it has been referred to as the “problem child of seasonal flu”. It affects seniors more severely than other strains of flu and its rapid mutations mean that vaccines are not effective against it for long. As a result, if H3N2 is prevalent, it may well increase the number of excess winter deaths.
The key questions are:
- Can we predict years of heavy winter mortality by monitoring common strains of flu in other parts of the world?
- How much should we allow variation in the annual number of deaths due to factors such as the prevalent strain of flu feed into longevity projections?
What do you think?
Please post your questions in our Friends of Club Vita discussion group on LinkedIn.
Top Charts Issue 15: Flu strains and excess winter deaths
Download a print friendly version of this article.