Currently there is debate as to whether we are in phases 3,4 or 5 of a pandemic. Best to read the
As of early August 2005, most sources place the current avian
influenza epidemic at phase 3. There is ongoing debate as to the
current phase. As of late September 2005 consensus had not been reached
on what the current phase should be considered (between 3-5) based on
the ongoing outbreaks in multiple countries of southeast asia. The
phases are defined as:
Interpandemic period
Phase 1: No new influenza 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 be low.
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
Phase 3: Human infection(s) with a new subtype, but no human-to-human spread, or at most rare instances of spread to a close contact.
Phase 4: 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).
Pandemic period
Phase 6: Pandemic: increased and sustained transmission in general population.