What is the current state of alert?

The swine flu alert level from the World Health Organization (WHO) remains at Phase Five, which means there is human-to-human spread of the virus in at least two countries in the same region. Phase Five is a strong signal that "a pandemic is imminent and that the time to finalise the organisation, communication, and implementation of planned mitigation measures is short," says the WHO. This is something that is already well under way in the UK.

As further information becomes available, WHO may decide to either revert to Phase Four or raise the level of alert to Phase Six, the highest level. The decision to move to Phase Five was based primarily on data demonstrating sustainable human-to-human transmission of the virus.

The WHO has defined six stages in the development of a pandemic. A virus outbreak is only classified as a pandemic at Phase Six.