Lee, a South Korean and 23-year WHO veteran, died two days after undergoing emergency brain surgery as the annual World Health Assembly got under way in Geneva last month. He was the first WHO director-general to die in office.

The quest for a new leader of the global body is now in full swing, with elections set on November 9 at a special World Health Assembly of its 192 member states.

As the official campaigning began on June 19, the candidate from Asia said he was the man for the job. Widely respected by his peers, the softly spoken Dr Omi is a 16-year WHO veteran who's been nominated by the Japanese foreign ministry, which described him as 'well-suited for the post'.

Dr Omi studied law at Keio University in Japan and later obtained a degree in medicine from Jichi Medical School, before completing a doctorate in the molecular biology of the hepatitis B virus.

After working as a medical officer at the Tokyo city government, he joined the WHO western Pacific regional office in Manila in 1990 and became regional director in February 1999.

'Many people have told me I'm a leader who has already been tested by public health [crises] and found to be equal to the challenges,' said Dr Omi, who, if successful, would be the third Asian to take the job.

Two other possible contenders for the position are Julio Frenk, the Mexican health minister, and Belgium's Peter Piot, the head of UNAids. Both stood for the post in 2003, but were beaten by Lee. Informed sources said that Dr Piot, who had been expected to provide a strong challenge to Dr Omi, was unlikely to stand.

The other candidates in the 2003 race were Dr Pascoal Manuel Mocumbi of Mozambique, and Professor Ismail Sallam of Egypt.

Sweden's Dr Anders Nordstrom will continue as acting director-general of WHO until a new director-general takes office. He cannot stand for the position, after pledging not to when he took on the interim role.

Lee, who was 61 when he died, was the sixth WHO director-general, and the second Asian - after Japan's Hiroshi Nakajima who filled the role from 1988-1998 - to take the post.

He succeeded the feisty former Norwegian prime minister, Gro Harlem Brundtland, in July 2003, at the tail end of the global outbreak of Sars, which tested the international network's response to a spreading new infectious disease.

During Lee's brief term, the WHO ratified the Framework Convention on Tobacco Control (the first public health treaty negotiated by WHO), adopted a revised set of International Health Regulations, and led the health response to the Asian tsunami and the Pakistan earthquake.

More than anything else, Lee's term had been defined by bird flu and the initial global response that the agency was able to harness to try to control H5N1 flu at source before it spreads to humans.

The WHO has pushed countries to design and test pandemic flu preparedness plans; it has stockpiled the flu treatment Tamiflu, and has liaised with pharmaceutical companies on possible pandemic flu vaccine development.

In efforts at bridge-building, Lee named Liu Peilong, from China's Ministry of Health, as assistant director-general and an adviser to him at WHO.

Margaret Chan Fung Fu-chun, who was Hong Kong's director of health from 1994 to 2003, and alerted the world about H5N1 flu in 1997 and Sars in 2003, became an assistant director-general on communicable diseases and his representative on pandemic influenza.

A Beijing funding summit in January also was able to generate a commitment of US$1 billion for the global flu plan, although so far US$300 million has reportedly been received.

With his death, Lee's strategy against pandemic flu has been left untested, and it's now up to the next director-general to improve on it and perhaps make the critical decision that could save a significant proportion of the world's population if or when a flu pandemic occurs.

Although H5N1 has essentially remained an animal disease, it has killed 130 people among 228 cases in 10 countries since 2003, according to the WHO. Worst hit is Asia, with Vietnam tallying the most cases so far and Indonesia - still battling outbreaks - not far behind.

Scientists fear bird flu could become highly dangerous to humans if the virus mutates into a form easily passed on from one person to another.

China, moreover, has remained a largely covert operation, critics say. Last week, a team of eight mainland doctors reported in a research letter in the New England Journal of Medicine that a 24-year-old Beijing man who died of pneumonia in November 2003, and was at first suspected to be a Sars victim, in fact died of bird flu. 'All tests were negative for Sars,' the report said.

If the man had bird flu rather than severe acute respiratory syndrome, it would mean the current H5N1 outbreak in Asian poultry, thought to have begun in South Korea in December 2003 and to have spread to humans in Vietnam that month, started earlier on the mainland.

China also has yet to share animal viruses detected in their outbreaks, and has not shared most of the virus samples from Chinese people infected, despite WHO urging. The mainland has reported 19 people with H5N1, of whom 12 have died.

Concern has also been raised in Indonesia, where bird flu was spread directly between members of a northern Sumatra family in the first laboratory confirmed case of human-to-human transmission of the virus. The findings also provide the first confirmation of a three-person chain of infection. Indonesia is a member of the WHO Southeast Asia region, which is run by another regional director.

The director-general chosen to head the WHO is supported by the WHO secretariat, which is staffed by about 3,500 health and other experts and support staff on fixed-term appointments. They work at the Geneva headquarters, in the six regional offices and in member countries.

Dr Omi, who has taken a leave of absence from his job for the sake of fairness and accountability, said the western Pacific region had done 'an excellent job' against bird flu.

The region is the largest, with 37 countries and areas, including the mainland and Hong Kong. It's home to 1.8 billion people and to some of the world's most advanced economies as well as some of the weakest.

'I was among one of the few who first alerted the international community,' Dr Omi said. He also recognised early on the need for collaboration of the health and agricultural sections in responding to bird flu, he said.

Speaking from Tokyo, where he will be based until the elections, he said he'd shown the 'technical leadership' when a public health response in the region was mounted successfully against Sars.

'I've also shown my ability to address some of the politically sensitive issues such as balancing member states' [interest] against the need for public health,' he said, citing the decision that WHO made to impose a travel advisory against Hong Kong and Guangdong on April 2, 2003.

'Many people told me that my track record as a public health leader speaks for itself,' he said.

Dr Omi said he saw this as an 'unexpected opportunity to bring commitment, dynamism and new leadership' to ensure WHO strengthens its role as the leading agency for health. 'I would like to stand for strong leadership with accountability. The circumstances of my candidature are very tragic because of the sudden demise of Dr Lee.

'We must push forward in confronting the many challenges of global health.'

Dr Omi is due to finish his current job in 2009 - unless he wins the top position.