 | Ten things you should know about pandemic influenza [WHO headquarters] | |
| How pandemic virus emerges | |
| History of influenza pandemics | |
An influenza pandemic can be defined as a global epidemic of influenza and it occurs when a new influenza virus (i.e. an influenza virus subtype that is not circulating widely in human beings) emerges and starts spreading in a similar way to normal influenza - through coughing and sneezing. Because the virus is new, the human immune system will have little or no pre-existing immunity. People who contract pandemic influenza are thus likely to experience more serious disease than that caused by normal influenza.
Avian influenza refers to a large group of different viruses that primarily affect birds. On rare occasions, these viruses can infect other species, including pigs and human beings. The vast majority of avian influenza viruses do not infect humans. Since 1997, avian influenza A(H5N1) has crossed the species barrier and infected humans on numerous occasions, causing severe disease and death. It therefore has pandemic potential, since it might ultimately adapt into a strain that is sustainably transmitted among human beings. Should such an adaptation occur, the virus will no longer be an avian virus, but a human influenza virus.
A pandemic is considered inevitable and its severity is unpredictable. Nevertheless measures can be taken to avoid the harm a pandemic may do to health and society as a whole. Countries all over the world are therefore encouraged to establish pandemic influenza preparedness, as proper planning may reduce morbidity and mortality, as well as mitigate the overall impact on society.
