Many hard-hit nations that have begun cautiously reopening have not seen spikes in new cases. But the U.S. has.  

As COVID-19 began to sweep the world in mid-March, health policy officials emphasized the importance of flattening the curve.

By the start of April, it appeared the United States was successful. Between April 19 and May 31, the number of new cases did not increase during a single week.

The other three countries ranking in the top five in total confirmed cases (Russia, Italy, and Spain) have largely flattened their curves. They have mostly exhibited declines in new cases, with the exception of Brazil, which only now appears to be peaking,

But as the U.S. begins to enter the second and third phases of re-opening, we are once again seeing an uptick in new cases that the other heavily-hit countries have not seen. 

During the week of June 14, the United States saw 1.14 million new cases (a 12.7% increase compared to the prior week). For comparison, Italy has not seen new cases increase since the week of March 22. 

There are multiple theories about why other countries are not seeing a resurgence despite loosening regulations. But there are no clear answers yet.