THE first confirmed case of human-to-human transmission of Asian bird flu was announced as 快猫短视频 went to press.
The 40 people who have caught the H5N1 virus so far appear to have been infected by birds. But on Tuesday the authorities in Thailand announced that a girl infected by chickens in the northern province of Kamphaeng Phet passed the virus to her mother.
The virus may not yet be easily transmissible between humans, and may only have spread in this case because the family members were in extended close contact.
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But if it does mutate and become more infectious, the chances of preventing a pandemic look slim. People can transmit flu before symptoms start, so isolation and quarantine would accomplish little, says D. A. Henderson, who advises the US government on biosecurity.
The US is the only country to have announced plans to produce large-scale supplies of a human vaccine against H5N1. It is unclear how effective the vaccine will be, but so far it is the only one there is.
The US government said last week that it will pay the French firm Aventis-Pasteur, to make 2 million doses in case the outbreak triggers a human flu pandemic. It should be ready by December.
鈥淕lobally, the amount of vaccine that could be produced, even under heroic conditions, would be but a gesture,鈥� Henderson says.
The main hope for treating infected people is the antiviral drug oseltamivir. But Hiroshi Oshitani of the World Health Organization鈥檚 east Asian office told 快猫短视频 that the drug had 鈥渘ot been very effective鈥�. That may be because infections have not been caught early enough, he says.
The H5N1 vaccine will be the first flu vaccine produced on a commercial scale developed using 鈥渞everse genetics鈥�, a technique for mixing and matching genes from different virus strains (快猫短视频, 28 February, p 36). So far only small batches for use in clinical trials have been produced by Aventis-Pasteur and the biotech firm Chiron. Previous research suggests vaccines based on the H5 virus family give some immunity but they may be less effective than vaccines used to treat standard flu.
Aventis-Pasteur鈥檚 product is a hybrid of H5N1 isolated from a Vietnamese patient earlier this year and a fast-growing flu strain used in standard flu vaccine. The US government鈥檚 $13 million order will be made at an Aventis-Pasteur plant in Swiftwater, Pennsylvania, which is between production runs of its standard flu vaccine.
鈥淚f a pandemic of H5N1 occurred in humans the new vaccine would be used to protect laboratory workers, public health personnel and, if needed, the general public,鈥� says Tommy Thompson, the US Secretary of Health.
The estimated 420,000 hospital staff needed to maintain basic medical services in the US are a priority, not only to care for the sick but also because they would accelerate the spread of the virus if they became infected. But just who else gets vaccinated might be hard to decide if a pandemic becomes imminent.
Bruce Gellin, head of the US national vaccine programme, says: 鈥淭he decision on how to use it will be based on the clinical studies and global situation.鈥�