Pandemic influenza

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Influenza pandemics have occurred in:

  • 18891892 Appears to have been a H2N2 strain
  • 1900 May have been H3N8 although N8 has not shown sustained transmission in man recently
  • 1918 Spanish influenza an H1N1 strain
  • 1947 Caused by major H1N1 drift and some question true pandemic. The vaccine failure of the widely deployed 1945 vaccine was spectacular.
  • 1957 Asian influenza an H2N2 strain
  • 1968 Hong Kong influenza an H3N2 strain
  • 1977 Russian flu, so called pseudo-pandemic of an H1N1 virus that some think came from a 1950 frozen isolate due to lack of antigentic drift for decades[1][2] but it could have been a reassortment virus that had been in unknown animal reservors[3].
  • 2009 Swine influenza

There are historic references to upper respiratory tract symptom associated epidemics back to ancient Greece (Hippocrates) and certainly in the Middle Ages.

The existence of a pandemic is characterised by certain WHO influenza phases. Pandemics are probably usually related to multiple recombinant events in multiple species over a year or two before they emerge[4].

To a degree seasonal flu is related to pandemic influenza and certainly after a pandemic it is usual for the pandemic virus to be active seasonally for a time. Seasonal influenza tends to be about 75% influenza A and 25% influenza B. Pandemics are driven by a single strain.


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