This was due to a reassortment event that caused a minor clade to provide a haemagglutinin gene that later became part of the dominant strain in the 2002–2003 flu season.

A/Fujian (H3N2) was made part of the trivalent influenza vaccine for the 2004-2005 flu season and its descendants are still the most common human H3N2 strain.

"Through a reassortment event, a minor clade provided the haemagglutinin gene that later became part of the dominant strain after the 2002–2003 season.

[10] A/Fujian (H5N1) bird flu is notable for its resistance to standard medical countermeasures, its rapid spread, what it tells us about the continuing evolution of the H5N1 virus, and the political controversy surrounding it.

The rise of the Fujian-like strain seems to be the cause of increased poultry outbreaks and recent human cases in China, according to the team from the University of Hong Kong and St. Jude's Children's Research Hospital in Memphis.

Purification is far more expensive than the work in eggs, Dr. Stöhr said; a modest factory for human vaccine costs $100 million, and no veterinary manufacturer is ready to build one.

Also, poultry vaccines are "adjuvated" – boosted – with mineral oil, which induces a strong immune reaction but can cause inflammation and abscesses.

'Chickens are smaller and you only need to protect them for six weeks, because that's how long they live till you eat them,' said Dr. John J. Treanor, a vaccine expert at the University of Rochester.

"[18] Referring to the Fujian-like strain, an October 2006 National Academy of Sciences article reports: "The development of highly pathogenic avian H5N1 influenza viruses in poultry in Eurasia accompanied with the increase in human infection in 2006 suggests that the virus has not been effectively contained and that the pandemic threat persists.

[...] Serological studies suggest that H5N1 seroconversion in market poultry is low and that vaccination may have facilitated the selection of the Fujian-like sublineage.

The predominance of this virus over a large geographical region within a short period directly challenges current disease control measures.

"All the analyzed Fujian-like viruses had molecular characteristics that indicated sensitivity to oseltamivir, the first-choice antiviral drug for H5N1 infection.

In addition, only six of the viruses had a mutation that confers resistance to amantadine, an older antiviral drug used to treat flu.

"[19] The October 2006 National Academy of Sciences article also says: "Updated virological and epidemiological findings from our market surveillance in southern China demonstrate that H5N1 influenza viruses continued to be panzootic in different types of poultry.

Genetic and antigenic analyses revealed the emergence and predominance of a previously uncharacterized H5N1 virus sublineage (Fujian-like) in poultry since late 2005.

These viruses have already transmitted to Hong Kong, Laos, Malaysia, and Thailand, resulting in a new transmission and outbreak wave in Southeast Asia.

[citation needed] H5N1 has mutated[21] through antigenic drift into dozens of highly pathogenic varieties, but all currently belonging to genotype Z of avian influenza virus H5N1.

[23] Results reported by Dr. Webster in July 2005 reveal further progression toward pathogenicity in mice and longer virus shedding by ducks.

Clade 2 viruses were first identified in bird isolates from China, Indonesia, Japan, and South Korea before spreading westward to the Middle East, Europe, and Africa.

Genetic analysis has identified six subclades of clade 2, three of which have a distinct geographic distribution and have been implicated in human infections: On 18 August 2006, the World Health Organization (WHO) changed the H5N1 avian influenza strains recommended for candidate vaccines for the first time since 2004.

Recognition of the three new subclades means researchers face increasingly complex options about which path to take to stay ahead of the virus.

[28][29][30][31] According to the CDC article H5N1 Outbreaks and Enzootic Influenza by Robert G. Webster et al.:"Transmission of highly pathogenic H5N1 from domestic poultry back to migratory waterfowl in western China has increased the geographic spread.

While a World Health Organization official in China renewed previous complaints that the Chinese have been stingy with information about H5N1 in poultry saying "There's a stark contrast between what we're hearing from the researchers and what the Ministry of Agriculture says.

[13] Also in November, Margaret Chan, a former top government health official for Hong Kong, was made Director-General elect of the WHO.

The Chinese government said they "would fully support her work in the WHO so that she could wholeheartedly carry out her responsibility and serve the health cause of the world.