There are now more than 13 million confirmed coronavirus cases worldwide, according to Johns Hopkins University, with more than a quarter of them in the United States.

The surge in COVID-19 cases has prompted states to take action.

Restrictions on indoor activities have been reinstated in New Mexico, Oregon and California.

"The sectors that we're closing statewide, again, restaurants, wineries, movie theaters, family entertainment, zoos, museums, cards rooms and bars, to outdoor activities to the extent possible," said California Gov. Gavin Newsom.

Most U.S. states are seeing new weekly cases rise and health experts expect that trend to continue.

"I don't see how this ends. These numbers will keep going up. We'll go way past 100,000 new cases a day," said Dr. Peter Hotez, of Baylor College of Medicine.

Some of those new cases will be from the younger part of the population. Research published this week in the Journal of Adolescent Health says roughly a third of 18 to 25-year-olds are at risk of severe COVID-19.

"You go to school, you're going to come in contact with more people, so even if they're transmitting at a lower rate than adults, it may get washed out or increased essentially because they have more contacts," says CNN Chief Medical Correspondent Dr. Sanjay Gupta.

Amid the crisis, the Trump Administration is pushing for schools to reopen later this year. Some teachers and parents are concerned.

"For the first time in my 17-year career, I'm scared. And I'm not scared because of curriculum. And I'm not scared because of changes. I'm scared for my own safety and for my children's safety," says elementary school teacher Sara Voss.