这可能是由于1977年的一次意外：当时前苏联偶然泄露了一株季节性H1N1流感病毒，此后这病毒便与通常流行的H3N2流感病毒株一起扩散开来。
We have this immunity because of a biological accident: in 1977, an H1N1 flu virus was accidentally released in the Soviet Union and has circulated ever since, alongside the regular H3N2 strains.
数据安全——数据安全是指数据在采集、传输、存储、交换过程中，非偶然或者恶意原因而遭受破坏、更改、泄露。
Data security - data security refers to the data in the collection, transmission, storage, exchange process, non accidental or malicious reasons for damage, change, disclosure.
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