(CNN) For anyone still wondering whether this surge in new Covid-19 cases is real -- or if it just looks that way due to increased testing -- a Trump administration official put that question to rest Monday.
"There is no question we are having a surge right now," said Adm. Brett Giroir, the US assistant secretary of health who's leading the administration's Covid-19 testing efforts.
"Yes, we are having increased cases, predominantly in the Sun Belt," Giroir said. "We are having more cases than we did a week ago, two weeks ago, three weeks ago, four weeks ago. That is very clear."
As of Monday morning, 31 states have seen more new cases this past week, compared to new cases from the previous week, according to data from Johns Hopkins University.
And some places are getting overwhelmed with new hospitalizations or deaths.
Now, some local officials are reluctantly considering another shutdown.
"It's not just what's opened and closed, it's also about what we do individually," Garcetti said.
"It's about the people who are getting together outside of their households, with people they might know. It might be their extended family, it might be friends. They might think because they got a test two weeks ago, that it's OK. But it's not."
California Gov. Gavin Newsom said hair salons and barbershops in 33 counties on a monitoring list may now reopen outside under new guidance from the state.
"Outdoor operations may be conducted under a tent, canopy, or other sun shelter as long as no more than one side is closed, allowing sufficient outdoor air movement," according to the guidance.
Across the country, more than 3.7 million Americans have been infected with Covid-19, and more than 140,811 people have died, according to data from Johns Hopkins University.
Positive results from three vaccine trials reported Monday offered some rays of hope.
Results from a Phase 1/2 trial published in the journal The Lancet suggest a University of Oxford and AstraZeneca vaccine is safe and induces an immune response to the virus.
The results were "at the high end of our expectations," Adrian Hill, the lead researcher in the trial, told CNN's Kate Bolduan on Monday.
The key question is whether that response is "strong enough, potent enough, to stop this infection happening," Hill said.
In animal data, the answer is probably yes, he said, "but humans could be different." The trial involved 1,077 people.
"In terms of how long it will last, we're less concerned about that. We've used this vaccine type before. Immunity is durable, certainly for a year, probably for longer than that," Hill said.
More Phase 2 results published Monday on CanSino Biologics' vaccine suggest it is safe and created an immune response. The trial involved more than 500 people given high, low or placebo doses of the vaccine.
It's not yet clear whether any would protect people from the virus in the real world. Large Phase 3 trials expected to begin in the coming months are needed to determine whether they work.
While many governors are reluctant to shut down their states again, many are turning to mask mandates instead.
In Colorado, Gov. Jared Polis said his state noticed decreased spread of the virus in places where more people wore face masks. Polis issued a face mask mandate statewide that took effect July 17.
"With the desire to keep the economy open, to maximize the ability to return to school in as safe a way as possible for teachers and for students, the mask mandate was really an easy decision after I saw that data," Polis told ABC's "This Week."
Doctors and scientists have repeatedly said masks are among the most powerful weapons Americans can use against the virus.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, has urged governors and mayors to be "as forceful as possible" to get Americans to wear face coverings.
In Florida, where daily new cases have tripled in a month, the governor has resisted implementing a mandate and said the state would not be prosecuting people who don't wear face coverings.
But in Miami, officials are doubling down on an existing mask order. Starting Monday, residents who fail to wear a face mask in public will be fined without first getting a warning. That fine starts at $50 and will increase at every additional offense.
With more states reporting surges, local leaders are scrambling to figure out whether or how to get kids back in school.
President Donald Trump has already said he has pressured governors to ensure a return to classrooms across the country in the fall.
In Arizona, 87 health care professionals signed a letter urging the state leader to keep schools closed for the first quarter of the school year. The governor has indicated he'll give more guidance on school reopenings in the coming days.
"We share a common concern: that the tremendous pressure to return to in-person schooling in August is ill-advised and dangerous given the uncontrolled spread of Covid-19 in our community," the letter said.
The researchers in South Korea also found that children ages 9 and younger transmitted the virus within their household at rates that were a lot lower.
"Although the detection rate for contacts of preschool-aged children was lower, young children may show higher attack rates when the school closure ends, contributing to community transmission of Covid-19," the study said.