Bird Flu - Pandemics
Much of the concern over bird flu has centered on continuing reports that the world experiences an influenza pandemic every few decades or so, and that we are “overdue” for another.
The US Centers for Disease Control and Prevention say:
An influenza pandemic is a global outbreak of disease that occurs when a new influenza A virus appears or “emerges” in the human population, causes serious illness, and then spreads easily from person to person worldwide. Pandemics are different from seasonal outbreaks or “epidemics” of influenza. Seasonal outbreaks are caused by subtypes of influenza viruses that are already in existence among people, whereas pandemic outbreaks are caused by new subtypes or by subtypes that have never circulated among people or that have not circulated among people for a long time. Past influenza pandemics have led to high levels of illness, death, social disruption, and economic loss.
There were three global flu pandemics in the 20th century:
Spanish Flu, 1918-19
Originating in Europe and the US, this swept the world at the end of World War I, killing an estimated 40 million to 50 million people (compared to some 8.3 million military deaths during the war). It is regarded as one of the most deadly disease events in human history.
Asian Flu, 1957-58
This flu, starting in China, was milder than the Spanish flu pandemic, and medical science was more advanced. The number of deaths is estimated at around two million.
Hong Kong Flu, 1968-69
This also started in China, though was milder than the Asian flu, and global deaths were probably around one million.
In May 2005, the World Health Organization published its WHO Global Influenza Preparedness Plan. It identified six stages of a pandemic:
– No new virus subtypes have been detected in humans. An influenza virus
subtype that has caused human infection may be present in animals. If
present in animals, the risk of human infection or disease is considered to
Phase 2 – No new influenza virus subtypes have been detected in humans. However, a circulating animal influenza virus subtype poses a substantial risk of human disease.
Pandemic Alert Period
– Human infection(s) with a new subtype, but no human-to-human transmission,
or, at most, rare instances of spread to a close contact.
– Small cluster(s) with limited human-to-human transmission but spread is
highly localized, suggesting that the virus is not well adapted to humans.
Phase 5 – Larger cluster(s) but human-to-human spread still localized, suggesting that the virus is becoming increasingly better adapted to humans, but may not yet be fully transmissible (substantial pandemic risk).
Phase 6 – Pandemic: increased and sustained transmission in general population.
WHO itself has said that the world is currently in Phase 3, though some experts believe we are in Phase 4, and possibly even Phase 5.