https://blog.wongcw.com/2021/12/02/%e5%8d%97%e9%9d%9e%e5%b0%88%e5%ae%b6%ef%bc%9aomicron%e5%82%b3%e6%9f%93%e6%80%a7%e5%be%88%e5%8f%af%e8%83%bd%e8%b6%85%e9%81%8edelta/