Now, the bad news: In many of those states, testing has also decreased. And the overall number of daily new cases is still way too high as the U.S. faces a trio of major challenges this fall.
"The fall is really not going to look very good," epidemiologist Dr. Celine Gounder said.
On Sunday, 34,450 new cases were reported nationwide, according to data from Johns Hopkins University. That's better than the summer peak in late July, when the U.S. had more than 60,000 new cases a day.
But nationwide, testing is down 10% this past week compared to the previous week, according to data from the COVID Tracking Project.
And of the confirmed cases we do know about, 34,450 is still an enormous number, health experts said Monday.
"We never really got the cases down. Remember, we're talking about 35,000 cases a day. Today, we're likely to hit over 40,000 cases a day," said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota.
"Back in April ... we had 22,000 cases a day and thought, 'My God, it can't get any worse.' And what's happening here is we're going to see this kind of up-and-down, up-and-down. But each time it goes up, it goes a little higher. Each time it comes down, it doesn't come down as far."
By Monday evening, more than 6.5 million people have been infected with coronavirus in the U.S., and more than 194,000 have died, according to Johns Hopkins data.
Nearly 550,000 children in the U.S. have been diagnosed with COVID-19 since the pandemic began, according to the American Academy of Pediatrics and the Children's Hospital Association.
The groups found that children represent nearly 10% of all reported cases in the U.S.
3 big challenges this fall
Epidemiologists say the U.S. must get the virus under control because the U.S. will soon face several challenges simultaneously:
And having one of the two viruses can make you more vulnerable to getting infected with the other.
"You're going to have all these patients coming into hospitals and doctors office with symptoms that could be coronavirus, that could be the flu," Gounder said.
"And we're going to have to treat all of them like they have coronavirus. So that's a very dangerous and scary situation to be in."
Athens-Clarke County, Georgia — home to the University of Georgia — has seen a "dramatic spike" in cases after maintaining lower case counts and death counts throughout the summer, Mayor Kelly Girtz said.
"Clearly, it's the return to campus of large numbers of students who are not here through the summertime," the mayor said.
Michigan State University students were asked to quarantine after the local health department reported 342 new cases among people affiliated with the university since Aug. 24, East Lansing Mayor Aaron Stephens said.
Some good news on the vaccine front
While health experts stress that a COVID-19 vaccine might not be publicly available until 2021, there are promising signs among several of the vaccines currently in Phase 3 trials.
Pfizer CEO Albert Bourla told CBS' "Face the Nation" that there was a "quite good chance" researchers will know by the end of October whether its experimental vaccine works.
"Then, of course, it is (the) regulator's job to issue (a) license or not," Bourla said.
The University of Oxford announced its trial would resume in the United Kingdom after being halted due to an unexplained illness in one of the volunteers. Experts say it's not unusual for trials to be halted.
And vaccine makers are reporting progress with recruiting minority trial participants, which has been a struggle in recent weeks.
"I think we should strive to have a more diverse population as possible," Bourla told CBS, stressing the importance of having a diverse group of volunteers given the heightened impact COVID-19 has had on communities of color.
"Right now we are not bad. Actually, we have a population that globally only 60% are Caucasians, 40%, approximately, minorities."
Moderna, which is also in Phase 3 testing for its vaccine, said its minority enrollment has also improved. About 59% of the participants are White, 22% are Hispanic, 11% are Black, 5% are Asian, and 3% are from other populations.
It could take years to vaccinate everyone worldwide
The world's largest vaccine manufacturer said if a COVID-19 vaccine requires two doses, it might be 2024 before everyone could get inoculated.
Adar Poonawalla, chief executive officer of the Serum Institute of India, told the Financial Times that if the vaccine needs two doses to work, the world would need about 15 billion doses.
And that means production on a mammoth scale.
"I know the world wants to be optimistic on it ... [but] I have not heard of anyone coming even close to that [level] right now," Poonawalla said. "It's going to take four to five years until everyone gets the vaccine on this planet."
Dr. William Schaffner, an infectious diseases professor at Vanderbilt University Medical Center, said he expects the timeline in the U.S. to be faster.
"I suspect we'll have more vaccine for the United States before we have it for the entire world," Schaffner said.
Several vaccine makers in the United States have given their volunteers two doses during at least one phase of their clinical trials.
But "some vaccines under development right now require only one dose," Schaffner said. "So I think that timeline could be accelerated -- surely here at home, and even around the world."