https://blog.wongcw.com/2021/06/06/%e7%a0%94%e7%a9%b6%e7%99%bc%e7%8f%becovid-19%e7%96%ab%e8%8b%97%e6%8e%a5%e5%8f%97%e8%80%85%e9%87%9d%e5%b0%8ddelta-b-1-617-2%e8%ae%8a%e7%a8%ae%e7%9a%84%e6%8a%97%e9%ab%94%e6%b0%b4%e5%b9%b3%e8%bc%83/