The two strains whose genes are found in the hybrid belong to influenza families known generally as North American and Eurasian pig flu.

在加利福尼亚病毒样本中发现的两种菌株的基因很常见，属于北美和欧亚猪流感株。

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The new virus has genes from North American swine influenza, avian influenza, human influenza and a form of swine influenza normally found in Asia and Europe, said Nancy Cox, chief of the CDC's Influenza Division.

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While we take a break from influenza during the North American summer, flu attacks the Southern Hemisphere, and in the tropics, flu rates are relatively stable throughout the year.

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This year's North American vaccine is made from three viruses: two types of influenza A virus (H3N2 and H1N1) and an influenza B virus.

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