So, that was a naturally occurring attenuated virus that could be produced into a vaccine that didn't cause the disease.

因为天花病毒存在天然的衰减病毒,这种衰减病毒可以用来,直接生产不致病的疫苗

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So, you couldn't introduce the live virus in because that would cause the disease not just immunity.

所以 不可以直接接种活体病毒,因为这会使人致病而不仅是引起免疫应答

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