Two weeks before Independence Day, the United States had a legitimate reason to celebrate. After more than a year of worry and restrictions that followed the emergence of the coronavirus, the number of new cases each day had fallen to a little over 11,000, the lowest level since the virus first emerged in March 2020. The rapid vaccination of millions of Americans had cut off potential hosts. Combined with warmer weather that pushed people outside, the virus was far less able to gain ground.

The COVID-19 curve in the U.S. is rising again after months of decline, with the number of new cases per day doubling over the past three weeks, driven by the fast-spreading delta variant, lagging vaccination rates and Fourth of July gatherings.

Confirmed infections climbed to an average of about 23,600 a day on Monday, up from 11,300 on June 23, according to Johns Hopkins University data. And all but two states — Maine and South Dakota — reported that case numbers have gone up over the past two weeks.

The number of daily new COVID-19 infections has shot up almost 50 percent in the United States amid the spread of the highly contagious Delta variant — with rises even recorded in states with high vaccination rates, data shows.

The US on Tuesday recorded an average of 19,455 new cases per day over the last seven days — up 47.5 percent from the previous week, according to a USA Today analysis of data from Johns Hopkins University.