* Says does not want to cause panic when announces level 6
* Stabilisation of cases should not lead to over-confidence
* Effect of new strain during southern winter unknown
MADRID, May 4 (Reuters) - The World Health Organisation is likely to raise its alert for the new influenza strain to the highest level and declare a pandemic, its head indicated in an interview published on Monday.
"Level six does not mean, in any way, that we are facing the end of the world. It is important to make this clear because (otherwise) when we announce level six it will cause an unnecessary panic," Margaret Chan, WHO Director General told Spanish newspaper El Pais.
"Flu viruses are very unpredictable, very deceptive...We should not be overconfident. One must not give H1N1 the opportunity to mix with other viruses. That is why we are on alert," she told the newspaper.
Chan warned against over-confidence following a stabilisation in the number of new cases of H1N1 because the southern hemisphere was about to enter winter when flu cases naturally spike.
"We have to be very careful. No one can predict what is going to happen when countries in the south have flu peaks and this new one arrives -- which it is going to do, without a doubt."
"It is true that the number (of cases in people who have not been to Mexico) is small but because of that I would say that we have not seen the full situation or the whole picture of what is happening. The situation is evolving and the virus is changing".
She said it was too early to predict what proportion of the population would catch the new influenza strain after the European Union predicted 40 percent of the population would become infected. (Reporting by Ben Harding)