'The pandemic will persist in the coming months as the virus continues to move through susceptible populations,' it said in a statement.

It advised countries in the northern hemisphere to prepare for a second wave of pandemic spread.

'Countries with tropical climates, where the pandemic virus arrived later than elsewhere, also need to prepare for an increasing number of cases,' it added.

According to WHO experts, there are currently no signs that the H1N1 virus has mutated to a more virulent or lethal form.