More and more A/H1N1 influenza infections are expected in the northern hemisphere as the cold season approaches, the World Health Organization (WHO) said on Thursday.

"We're entering into the cold season in the northern hemisphere...Certainly we expect more cases in the next few months," said Gregory Hartl, the UN agency's spokesman for infectious disease outbreaks.

"This is apparently a virus which is very transmissible, and it can easily infect many people. And there are still a lot of people out there to be infected," Hartl told Xinhua in a telephone interview.

According to the spokesman, flu cases are rising rapidly in many regions in the northern hemisphere, although the traditional peak period for influenza activities -- January and February – is still two months away.

"The fact that flu cases are rising right now, as we are moving toward January and February, is on the one hand not surprising. And on the other hand it is surprising, because it is earlier than normal," Hartl said.

He added that in most places around the world, the H1N1 virus is the dominant flu virus, "because this is a novel virus to which no one has immunity, and it spreads more easily."

The spokesman reiterated that vaccination is "one of the best tools" for countries to deal with the A/H1N1 pandemic, the first pandemic since 1968.

As to the measure of school closure, he said that could not stop the spreading of the virus, but could slow it down.

The A/H1N1 influenza has infected at least 414,945 people and caused some 5,000 deaths worldwide since it was first identified in North America in April, according to a WHO update last week.