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Some of the world’s leading vaccine makers are developing bird flu shots to prepare 【小题1】 possible outbreaks of the sickness in humans.

Bird flu, or avian (鸟类的)flu, is 【小题2】(official) known as H5N1. The virus usually 【小题3】(spread) among different kinds of poultry (家禽). Human infections remain very rare. But most human cases have been linked to direct contact with 【小题4】(infect) birds.

Now, several large vaccine developers 【小题5】(work) on bird flu vaccines to get ready for the possibility that the virus could one day jump to humans.

One current outbreak involves an avian flu version 【小题6】has already killed record numbers of birds and some other affected animals. In addition, there has been 【小题7】push among companies to develop a vaccine to be given directly to poultry. Such a market could be much 【小题8】(large) than the one for humans. Vaccine 【小题9】( professional) told Reuters that hundreds of millions of bird flu shots could be manufactured within months if a new variant (变种) of the virus starts spreading among humans.

An international agreement 【小题10】 (cover) pandemic flu sets aside 10 percent of worldwide supply for the World Health Organization to share with low-and middle-income countries.