backflow valve 应该五年换一次，否则sprinkler里的脏水会进入饮用水系统。我们家的backflow valve今年七月需要换。考虑到家里四个大人（包括两个老人）都已经打了第二针疫苗，10岁的小孩还没有打疫苗。是不是现在就请plumber来换backflow valve？ 主要考虑七月的时候病毒的变种肆虐，我们的疫苗已经没有保护作用了。还是指望七月甚至拖几个月疫情好转后再换backflow valve，大家怎么看？谢谢！ 这是今天CNN的新闻： Just one month ago, B.1.1.7 made up around 4% of coronavirus cases in the US, among those that have undergone genomic sequencing. "Today, it's up to 30 to 40%," Osterholm told NBC on Sunday. "And what we've seen in Europe, when we hit that 50% mark, you'll see cases surge."
这是今天CNN的新闻： Just one month ago, B.1.1.7 made up around 4% of coronavirus cases in the US, among those that have undergone genomic sequencing. "Today, it's up to 30 to 40%," Osterholm told NBC on Sunday. "And what we've seen in Europe, when we hit that 50% mark, you'll see cases surge."
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