Health officials have major concerns as the COVID-19 delta variant continues to spread across the country and many Americans are not getting vaccinated.

The U.S. saw an average of more than 26,000 new COVID-19 cases over the last week -- a 67% hike from the previous week.

On top of that, not enough Americans are rolling up their sleeves to get a shot, especially the younger population.

"What we're seeing right now is a lot of young people getting sick from COVID, and not just that. They're developing very severe disease and needing to be hospitalized in the ICU…there's the effect of long COVID that these young kids are going to have that we don't fully understand at this point," says emergency room physician Dr. Anand Swaminathan.

In response to the rise in COVID-19 cases, some areas are bringing back mask guidelines, including parts of California and Nevada.