H1N1 flu has now spread to some 160 countries, killing about 800 people, but its behaviour so far has not changed, the World Health Organisation said on Friday.
"For the moment we haven't seen any changes in the behaviour of the virus. What we are seeing still is a geographic expansion across countries," WHO spokesman Gregory Hartl told a news briefing.
Hartl said the first vaccine doses for the disease, commonly known as swine flu, should be ready in the northern hemisphere's early autumn.
The WHO so far has promises of 150 million doses from two manufacturers for developing countries and is negotiating with other producers for further doses which will be earmarked for the least developed countries, he said.