His successor, Yasuo Fukuda, has pledged to continue along the path of reform while addressing inequality.
The WHO also has no evidence of widespread resistance to antiviral medication, Fukuda said.
Yet, even if Mr Fukuda stands firm, he will have only made a start.
In 1978, Japanese Prime Minister Takeo Fukuda resigned after defeat in a party poll.
Keiji Fukuda, the assistant director-general of the World Health Organization, called the outbreak "serious" on Sunday.
In response, Mr Fukuda promised to revamp the programme and to scrap earmarked taxes.
Yet Mr Fukuda's survival hangs on people taking seriously his promise to face down pork-barrel interests.
As host, Japan's prime minister, Yasuo Fukuda, is determined to make the best of the contradictions.
Other useful protections against H1N1 are vaccines, which the WHO recommends against pandemic infections, Fukuda said.
The biggest loser so far has been Fukuda who fell out of the billionaire ranks in 2009.
It was Mr Fukuda, it is said, who brokered the recent diplomatic reconciliation with China, for instance.
"We continue to see human-to-human transmission, community transmission, primarily in North America, " said WHO Assistant Director-General Keiji Fukuda.
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Mr Oshima predicts that Mr Fukuda will now survive until an election must be called in September 2009.
Mr Aso, more hawkish than Mr Fukuda, is congenial and fairly popular, having worked the party's grass-roots organisations.
Late last month, Mr Fukuda called for a fresh diplomacy in Asia that built on his father's beliefs.
Prime Minister Yasuo Fukuda spent his early career at an oil company when crude was a dollar a barrel.
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"We welcome the announcement, " government spokesman Yasuo Fukuda said at a press conference.
But Mr Fukuda said the WHO "certainly has no recommendations on whether women should try to have children now".
Over the summer, it will become a little clearer whether Mr Fukuda has the gumption to push his agenda.
Mr Fukuda will possibly not be around in a year's time, with Mr Brown's future only a little less assured.
Mr Fukuda's approval ratings are now even lower in some polls than the low point of his predecessor, Shinzo Abe.
In Central America and the Southern Hemisphere, however, activity levels have dropped as those regions enter the summer season, Fukuda said.
Fukuda praised as "innovative" the decision by Norway to distribute antiviral medication over the counter for a limited period of time.
But contrary to some reports, Fukuda said, the WHO has not seen big mutations in the virus since it first emerged.
"East Asia is one of the parts of the world where seasonal influenza viruses have remained in reasonably high circulation, " Fukuda said.
Dr Fukuda led a team from the WHO on a one-week China visit to study H7N9, along with Chinese officials from Beijing and Shanghai.
In Australia, for example, "aboriginal groups are disproportionately represented in people who end up in hospitals from diseases related to the pandemic, " Fukuda said.
Soon after the summit, Mr Oshima expects, Mr Fukuda will shuffle his cabinet, whose members were largely inherited from Shinzo Abe, his hapless predecessor.
Mr Fukuda said officials and drug manufacturers were investigating how to speed up the process of developing a vaccine against the H1N1 swine flu strain.
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