The scene of the Labor Day holiday in the United States can not help but reminiscent of Memorial Day more than three months ago. At that time, the United States was about to usher in the summer, and many people had expected it to be the "Summer of Hope." Today, the "New York Times" and many other US media can't help but sigh: "The once-hopeful summer is over." At the beginning of this summer, the number of confirmed cases in the United States increased to less than 25,000. US President Biden declared at the time that the United States will get rid of the new crown virus on July 4. "The irony is that for most of May and June, everything went so well that all of us were talking about the end of the (epidemic)." John Swartz, an infectious disease expert at the University of California, Berkeley John Swartzberg said: "People are enjoying life again. Within a few weeks, everything fell apart."