As the virus has continued to spread without causing deaths or even large numbers of hospitalization, many experts have been questioning whether the new strain of flu is deadlier than normal seasonal flu and in almost half of the cases in the U.S. the source of exposure is unknown.

Australia's health department has confirmed 401 new flu cases, including 306 in the southwestern state of Victoria and the number is doubling every 2 days, with evidence of community spread - this say health officials might prompt the WHO to raise the pandemic alert level to 6.

Health officials in Britain have confirmed there were another 17 cases of the virus across the UK, bringing the total to 246. The new cases included one in Wales, which is believed to be the first swine flu case in the country, and two cases in Scotland.

Eton College one of Britain's top public boys' schools, once attended by Princes William and Harry is also under investigation and has been closed until 7 June along with a number of other schools around the country.

The Department of Health says the cases of swine flu in the UK had so far been mild, and there was not yet evidence of "widespread community transmission" but strategies adopted to slow the spread of the disease appear to have been effective.