When Texas reopened bars for the U.S.'s Memorial Day weekend last month, cooped-up millennials and Gen Zers took full advantage, flouting social distancing rules to pack clubs and pushing their credit card spending in the next two weeks back to 2019 levels.

That brief fling with a more fulsome economic reopening, replicated in southern states like Florida and South Carolina, has boomeranged into a resurgence of novel coronavirus cases in the U.S. that is now changing the nature of the pandemic and likely to test the strength of any broader economic rebound.

The United States recorded 45,242 new cases of COVID-19 on Friday, the largest single-day increase of the pandemic, according to a Reuters tally, bringing the total number of Americans who have tested positive to at least 2.48 million.