Pandemic influenza phases

Through its global monitoring, the World Health Organization can track emerging outbreaks and has the authority to declare the existence of a pandemic

pandemic is a worldwide epidemic of a disease. The World Health Organization formally categorises outbreaks into different phases. The last global influenza pandemic was the H1N1 swine flu pandemic, formally announced on 11 June 2009. It was declared over on 10 August 2010.

The different phases of an influenza pandemic

Pandemic influenza phases

Phases 13: Predominantly animal infections; few human infections.

Phase 4: Sustained human-to-human transmission.

Phases 56: Pandemic.

Post-peak: Possibility of recurrent events.

Post-pandemic: Disease activity at seasonal levels.


Source: World Health Organization

About this resource

This resource was first published in ‘Influenza special issue’ in October 2009 and reviewed and updated in January 2015.

Ecology and environment, Health, infection and disease
Influenza special issue
Education levels:
16–19, Continuing professional development