It is too early to declare that the swine flu pandemic has peaked worldwide and many more people could become sick with the virus this winter, the head of the World Health Organisation said in an interview published on Tuesday.

The swine flu outbreak has peaked in the United States, Canada and some other countries in the northern hemisphere, Dr. Margaret Chan, she told the Geneva daily Le Temps.

“It is too early to assert that we have passed the peak of the flu A pandemic at worldwide level,” she said. “Not all the countries are there yet. Winter is still long,” said Ms. Chan.

Africa and some poor countries in Asia have not seen a surge in the number of swine flu cases, which could be due to weak reporting or because the full outbreak there may be yet to come, she told the newspaper.

Over 11,500 people are known to have died from the disease since the outbreak began in April, according to WHO. Between 2,50,000 and 5,00,000 people die from regular flu each year.

When the U.N. 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.

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

“WHO has adopted a very cautious attitude, even more so because this has been the first pandemic since four decades,” said Ms. Chan.