The WHO says the H1N1 virus must be monitored continuously - the WHO's global influenza surveillance network linking laboratories in 97 countries will see to that but the WHO says current recommendations for the use of antivirals will not be changed at present.

The pandemic flu alert has been raised by the WHO to its highest level of 6, signifying that the first influenza pandemic since 1968 is under way and some experts have expressed concern that Tamiflu might be less effective than Relenza following widespread reports of resistance to Tamiflu by seasonal H1N1 flu, a distant relative of the new swine flu virus.

The U.S. Centers for Disease Control and Prevention (CDC) also says that the isolated case in Denmark did not merit a change in the recommended use of Tamiflu as it remains a relatively mild influenza.

It is estimated that at least 20 companies are currently making flu vaccines some of which are expected to be available in the coming months.