Pandemic Possible, not Inevitable

In response to available data on confirmed outbreaks of A/H1N1 swine influenza in the United States of America, Mexico, and Canada, the World Health Organization raised the level of influenza pandemic level from phase 3 to phase 4. What do these phases mean?

We were at Phase 3:

In Phase 3, an animal or human-animal influenza reassortant virus has caused sporadic cases or small clusters of disease in people, but has not resulted in human-to-human transmission sufficient to sustain community-level outbreaks. Limited human-to-human transmission may occur under some circumstances, for example, when there is close contact between an infected person and an unprotected caregiver. However, limited transmission under such restricted circumstances does not indicate that the virus has gained the level of transmissibility among humans necessary to cause a pandemic.

We are now at Phase 4:

Phase 4 is characterized by verified human-to-human transmission of an animal or human-animal influenza reassortant virus able to cause “community-level outbreaks.” The ability to cause sustained disease outbreaks in a community marks a significant upwards shift in the risk for a pandemic. Any country that suspects or has verified such an event should urgently consult with WHO so that the situation can be jointly assessed and a decision made by the affected country if implementation of a rapid pandemic containment operation is warranted. Phase 4 indicates a significant increase in risk of a pandemic but does not necessarily mean that a pandemic is a forgone conclusion.

There are only 6 phases to this pandemic scale, with the 6th phase meaning the actual pandemic is underway.

While a tad frightening, these swine flu developments offer some great teachable moments about how viruses spread and how evolution plays a part in how a flu virus works.

Aetiology and Effect Measure would be good sources for more information.