The number of swine flu deaths reported worldwide has jumped by more than 700 in just one week as the northern hemisphere winter approaches.
The World Health Organisation says more than 5700 swine flu deaths were reported by 25 October, compared to just under 5000 the week before.
The biggest rise was in the Americas where 4175 deaths have been reported, up 636 from the week before.
However the director of the United States Centres for Disease Control and Prevention, Dr Thomas Frieden, says the strain is not mutating like other flu viruses.
"Virtually all of the influenza we're seeing is still H1N1," he says. "Genetically the virus has not changed, it's still closely matched with vaccine."
Dr Frieden says there's no evidence of mutations that would suggest the virus could become more deadly.
WHO reports nearly half a million cases
The latest WHO figures show there have been 440,000 confirmed cases of the H1N1 virus worldwide.
Fatal cases in Europe climbed to at least 281, while those in Asia-Pacific rose to 1070.
But the agency said the actual number is likely to be significantly higher as many countries have stopped counting individual cases.
Ukraine meanwhile has shut all schools and banned public meetings for three weeks following its first swine flu death.
The Prime Minister Yulia Tymoshenko said there would also be restrictions on non-urgent travel between different parts of the country.
The virus emerged in Mexico in April and was declared a global flu pandemic on 11 June.