by John Le Fevre
According to the world's peak health body more than 28,000 cases of influenza A (H1N1) have been reported globally and over 141 confirmed deaths.
In at least two regions of the world the virus is spreading, with rising cases being seen in the UK, Australia, Japan and Chile.
One factor which prompted the move to a level six pandemic was that in the southern hemisphere, the virus seems to be crowding out normal seasonal influenza.
Influenza A(H1N1) first emerged in Mexico in April and has since spread to 74 countries.
WHO chiefs said the move did not mean the virus was causing more severe illness or more deaths, but the global nature of the outbreak, transmission and rate of infection is fulfilling the requirements of a pandemic.
Experts from the WHO say the current pandemic is moderate and causing mild illness in most people.