GENEVA (AP) – Many more people could become sick with swine flu this winter even though it has peaked in North America and some European countries, the head of the World Health Organisation said this week.

The worst of the swine flu outbreak is over in the United States, Canada, Britain and some other countries in the northern hemisphere, said Dr. Margaret Chan.

But there is still intensive flu activity in Egypt, India and elsewhere, she said.

"It is too premature and too early for us to say we have come to an end of the pandemic influenza worldwide," Chan told reporters. Health experts should monitor the pandemic for another six to 12 months, she said, adding that the virus could still mutate and become more dangerous.

Over 11,500 people are known to have died from the disease since the outbreak began in April, according to WHO. Between 250,000 and 500,000 people die from regular flu each year. When the UN health agency declared swine flu to be a pandemic in June, it described it as "moderate".

While most people recover from the illness without needing medical treatment, officials are also continuing to see severe cases in people under 65 – people who are not usually at risk during regular flu seasons.

As many countries have rolled out massive swine flu vaccination programmes, demand for swine flu shots in some European countries has been lower than expected, said Chan.

WHO is talking to these governments to see if superfluous vaccines can be shipped to developing countries, she said.

The agency has warned that the virus could have a devastating impact in countries across Africa with high numbers of people with health problems like malnutrition, AIDS, and malaria. Drug makers and countries have promised to donate nearly 190 million doses of vaccines to WHO, she said. The figure is up from about 150 million doses two months ago.

Chan acknowledged she had yet to get her own swine flu shot. Only just back from leave, she said she asked her medical service to find out where she can get vaccinated.

Since flu viruses constantly evolve, experts have feared swine flu could mutate into a more dangerous form.

"One thing we need to guard against is the sense of complacency," Chan said, adding that flu viruses are highly unpredictable.