Today,Merlefest lasts for four days, with more than 100 performers playing on 15 stages.
VOA: standard.2010.06.07
Some, like the smallpox vaccine on one exposure generates a very high response that lasts for many years so you don't need a boost.
有一些疫苗,比如接触一次天花疫苗后,人体就能产生高水平的免疫应答,并持续很多年,所以无需再次接种
Some, like the smallpox vaccine on one exposure generates a very high response that lasts for many years so you don't need a boost.
有一些疫苗,比如接触一次天花疫苗后,人体就能产生高水平的免疫应答,并持续很多年,所以无需再次接种
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