It is not generally appreciated that descendents of the H1N1 influenza A virus that caused the catastrophic and historic 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, adds to the complexity surrounding this persistent progenitor virus, its descendants, and its several lineages .
Comment: The 1918 influenza virus and its progeny, and the human immunity developed in response to them, have for nearly a century evolved in an elaborate dance; the partners have remained linked and in step, even as each strives to take the lead. This complex interplay between rapid viral evolution and virally driven changes in human population immunity has created a “pandemic era” lasting for 91 years and counting. There is little evidence that this era is about to come to an end.
If there is good news, it is that successive pandemics and pandemic-like events generally appear to be decreasing in severity over time. This diminution is surely due in part to advances in medicine and public health, but it may also reflect viral evolutionary “choices” that favour optimal transmissibility with minimal pathogenicity — a virus that kills its hosts or sends them to bed is not optimally transmissible. Although we must be prepared to deal with the possibility of a new and clinically severe influenza pandemic caused by an entirely new virus, we must also understand in greater depth, and continue to explore, the determinants and dynamics of the pandemic era in which we live
Morens DM, Taubenberger JK, Fauci ASThe Persistent Legacy of the 1918 Influenza Virus.N Engl J Med. 2009 Jun 29. [Epub ahead of print] View Abstract View Full Paper
