The number of new COVID-19 cases among children in the United States rose 40 percent in the last two weeks of July, according to a report released just weeks before tens of millions of students are scheduled to begin the new school year.

Health experts are keeping an eye on infections among younger children and teenagers as officials struggle with the thorny question of whether to reopen schools for in-person classes, adopt a virtual learning model or a hybrid of the two.

US President Donald Trump has pushed states to allow students to physically return to classrooms, but health officials have expressed caution about doing so in areas where cases have been rising sharply.

The new report, by the American Academy of Pediatrics and the Children's Hospital Association, found that more than 338,000 children have tested positive for COVID-19 since the onset of the US epidemic, with 97,078 new cases reported from July 6-30.

Most of the new infections in this group occurred in states in the US South and West, according to the report, which was based on data from 49 states, New York City, the District of Columbia, Puerto Rico and Guam.

It did not give a reason for the recent spike. Testing for the coronavirus overall has risen in the US and concerns about children as possible spreaders of the virus have been sparked by studies showing they can catch it. The American Academy of Pediatrics noted the data showed that severe illness due to COVID-19 appears to be rare among children.

While it is said that children are "virtually immune" to the coronavirus, studies and data show that while children are far less likely to die from COVID-19 than adults, they can still pass the infection on to others.

The US Centers for Disease Control and Prevention recently updated its guidance to recommend that schools reopen to some degree unless their communities were experiencing an uncontrolled or high rate of transmission of the virus.

Reopening is seen as a vital part of Trump's overall plan for restarting the economy and to help in his reelection bid. The nation's 98,000 public K-12 schools, with nearly 51 million children, are a major part of the economy.

Big share of employment

Senate Minority Leader Chuck Schumer, a New York Democrat, said at a press briefing on Friday: "If we don't open up the schools, you're going to hurt the economy significantly, because lots of people can't go to work."

With a workforce of about 8 million before the pandemic, K-12 public education is also one of the largest US employment sectors.

Total expenditure for schools was $721 billion for the 2018 fiscal year, according to US Census Bureau data. That's more than the US Defense Department's $671 billion budget that year, or the Pentagon's $705 billion request for fiscal 2021.

Despite the president urging schools to get students back into classrooms, on Aug 2, Deborah Birx, the White House's top coronavirus coordinator, said that in hard-hit areas: "We are asking people to distance-learn at this moment so we can get this epidemic under control."

Her colleague on the White House team, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, has said that he favors getting students back in class, citing the psychological impact of keeping them home as well as the role schools play in feeding children.

"The default position should be to try as best as you possibly can to open up the schools for in-person learning," Fauci said.

Children account for a tiny fraction of the more than 162,000 people who have died from COVID-19 in the United States. More than 5 million people in the country have been infected with the virus, representing about a quarter of the total worldwide cases.

Agencies contributed to this story.