THE international pandemic alert level of the World Health Organisation was last night raised to phase five of six amid the global outbreak of swine flu.

Phase five indicates that the disease is able to spread easily between humans. However, so far evidence of human-to-human transmission has only been seen in Mexico and Spain.

With an elevated pandemic alert level, WHO might also issue travel advisories, warning against non-essential travel to regions battling outbreaks, trade restrictions, the cancellation of public events or border closures.

:: Phase one, no viruses circulating among animals have been reported to cause infections in humans.

:: Phase two, an animal influenza virus circulating among domesticated or wild animals is known to have caused infection in humans.

:: Phase three, an animal or human-animal influenza virus has caused sporadic cases or small clusters of disease in people, but has not resulted in human-to-human transmission.

:: Phase four, verified human-to-human transmission of an animal or human-animal influenza virus able to cause community-level outbreaks.

:: Phase five, human-to-human spread of the virus into at least two countries in one WHO region.

:: Phase six, the pandemic phase, is characterised by increased and sustained transmission in the general population.

Should phase six be activated across the globe, the UK still has its own four alert levels which come into play.

:: UK alert level 1 No cases in the UK :: UK alert level 2 Virus isolated in the UK :: UK alert level 3 Outbreak(s) in the UK :: UK alert level 4 Widespread activity across the UK