Influenza pandemics have occurred in:
- 1889–1892 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 but it could have been a reassortment virus that had been in unknown animal reservors.
- 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.
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.
- ↑ Laver WG, Webster RG, Chu CM. From the National Institutes of Health. Summary of a meeting on the origin of pandemic influenza viruses. The Journal of infectious diseases. 1984 Jan; 149(1):108-15.
- ↑ Nakajima K, Desselberger U, Palese P. Recent human influenza A (H1N1) viruses are closely related genetically to strains isolated in 1950. Nature. 1978 Jul 27; 274(5669):334-9.
- ↑ Kozlov JV, Gorbulev VG, Kurmanova AG, Bayev AA, Shilov AA, Zhdanov VM. On the origin of the H1N1 (A/USSR/90/77) influenza virus. The Journal of general virology. 1981 Oct; 56(Pt 2):437-40.
- ↑ Smith GJ, Bahl J, Vijaykrishna D, Zhang J, Poon LL, Chen H, Webster RG, Peiris JS, Guan Y. Dating the emergence of pandemic influenza viruses. Proceedings of the National Academy of Sciences of the United States of America. 2009 Jul 14; 106(28):11709-12.(Link to article – subscription may be required.)