Santa Claus rolls up his sleeve at a Montreal vaccination centre. Public health officials are concerned about outbreaks after Christmas. (CBC)

Swine flu is winding down in North America and parts of western Europe, but flu activity continues to increase elsewhere such as in Asia, the World Health Organization said Friday.

"There appears to be two to three times more hospitalized cases and deaths in the United States and approximately four to five times more hospitalized cases and deaths in Canada during the winter season [than the summer season]," the UN health agency said in its weekly pandemic update.

"This would indicate that transmission of the virus has been much more widespread and intense during the winter, as predicted, but overall rates of severe illness have not changed compared to [the] Southern Hemisphere."

After five weeks of decline in recorded transmission of swine flu in the United States, the death rate due to pneumonia and flu has also started to decline for the first time in eight weeks, WHO said.

In past years, flu outbreaks have occurred in the week after Christmas, and public health authorities have expressed concern about the busy holiday travel season, when people crowd into airports.

"We won't be surprised if we see another uptick later this year or early next year when kids return to school from Christmas break," said Tom Skinner a spokesman for the U.S. Centers for Disease Control and Prevention (CDC).

A post-holiday increase happened during the 1957 flu pandemic, federal health officials in Canada and the U.S. have noted.

To date, it's estimated about one-third of Canadians have become immune to the H1N1 influenza A virus that causes swine flu, either because they had flu or were immunized. That leaves about 22 million Canadians who are still vulnerable to infection.

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In western Europe, flu activity has peaked or passed its peak in Belgium, Iceland, Ireland, Netherlands, Spain, Portugal, Italy, and Germany. France, where swine flu is rising, is an exception, but the impact on the health system there has been "moderate," WHO said.

Flu activity continues to increase in parts of central and southeastern Europe, including in Albania, the Czech Republic, Estonia, Greece, Hungary, Latvia, Poland, Romania, Montenegro, Slovenia, and Turkey.

Further east, rates appear to be declining in Georgia, Bulgaria, and Ukraine.

Declines have also been reported in the tropical regions of Central and South America and the Caribbean.

Flu activity has begun to increase in south and east Asia, including the north-western parts of India, as well as in Sri Lanka, Hong Kong and Chinese Taipai.

On Friday, Chinese health officials warned H1N1 could peak in the next few months as hundreds of millions of people return home for the traditional Chinese New Year in late January and February.

As of Dec. 6, more than 200 countries have reported laboratory-confirmed cases of pandemic H1N1 influenza, including at least 9,596 deaths, WHO said. The week ending Dec. 6 was the second consecutive week that growth in mortality slowed.

With files from The Associated Press