A Deadly Family: Influenza A(H1N1)

Remember when in 2009 Influenza A(H1N1), also known as the Mexican flu or Swine flu caused widespread alarm and people feared the they faced an pandemic like the one in 1918? The pandemic didn’t seem to materialize and the same people who were panicking before were now scoffing their governments for squandering public money on vaccines that weren’t needed in the end .

But what nobody knew at the time was that in reality it was a close call. A study[1] commissioned by the WHO showed that approximately 24% of the entire population of the world, including half of all schoolchildren, were infected with Influenza A(H1N1) during the first year of the pandemic in 2009, according to data from 19 countries. It is also thought the virus killed 200,000 people around the world.

[From: Morens et al: The Persistent Legacy of the 1918 Influenza Virus]

Descendents of the Influenza A(H1N1) virus that caused the pandemic of 1918-1919 have persisted in humans for more than 90 years and have continued to contribute their genes to new viruses, causing new pandemics, epidemics, and epizootics. The current international pandemic caused by a novel influenza A (H1N1) virus derived from two unrelated swine viruses, one of them a derivative of the 1918 human virus[2]. In other words: The 2009 Influenza A(H1N1) pandemic virus represents yet another genetic product in the still-growing family tree of this remarkable 1918 Influenza A(H1N1) virus.

Maybe, just maybe, the Influenza A(H1N1) virus from 2009 just needs one single mutation become as lethal as his grandfather was back in 1918.

[1] Van Kerkhove et al: Estimating age-specific cumulative incidence for the 2009 influenza pandemic: a meta-analysis of A(H1N1)pdm09 serological studies from 19 countries in Influenza and Other Respiratory Viruses - 2013 
[2] Garten RJ, Davis CT, Russell CA, et al. Antigenic and genetic characteristics of swine-origin 2009 A(H1N1) influenza viruses circulating in humans in Science - 2009