And we must not forget: drug-resistant strains of viruses and bacteria also travel well internationally.

我们必须记住：病毒和细菌的耐药株同样也能在国际上迅速传播。

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Influenza viruses constantly undergo genetic changes and require vaccines that match the circulating influenza strains to be effective, so seasonal influenza vaccines have to be modified annually.

流感病毒不断发生基因变化并需要符合正在传播的流感毒株的疫苗以便产生作用，所以每年必须调整季节性流感疫苗。

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Two different strains within a single subtype, two different influenza A subtypes(H1N1 and H3N2), or both influenza A and B viruses may cocirculate.

单一亚型内的两个不同菌种之间，A型流感病毒的两个不同亚型（H1N1和H3N2）之间，以及A型流感病毒和B型流感病毒之间均可以互相转染。

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For other infections, particularly viruses, the primary treatment options are: vaccination to prevent infection, antiviral agents that only work against specific viruses (sometimes only specific strains of viruses) and just doing the best you can do to keep a patient healthy and hydrated while their own immune system does the heavy lifting.

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New viruses are formed when two different strains infect the same cell and exchange whole genes - a process known as genetic shift.

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Twenty-two days after an egg is injected with one of the three strains, Chiron workers extract the fluid and isolate and inactivate the viruses.

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