Especially, he added, among the country's older population, which was prioritized early on for the shots.

Nearly 83% of Americans 65 and older have received at least one Covid-19 vaccine dose and nearly 70% are fully vaccinated, according to data from the Centers for Disease Control and Prevention.

"This pandemic now is really among young people and it is a very dangerous time to be unvaccinated in the country because it is spreading pretty efficiently among young people and unvaccinated people," Jha said.

Rochelle Walensky warned last month the country was seeing an increase in cases and hospitalizations, predominantly among younger unvaccinated adults.

And in Michigan, which battled a violent spring surge, hospitals saw more younger Covid-19 patients than ever before.

So it's critical that younger Americans get a shot as well, experts say, for both their own protection and to help the country reach widespread protection.

Governor: Young Oregonians hospitalized with 'severe' Covid-19

To help bring up vaccination numbers and suppress the spread of coronavirus, governors are now appealing to younger residents.

"Younger, unvaccinated Oregonians are now showing up in our hospitals with severe cases of COVID-19," Brown said in a statement.

On Monday, he added officials are now also focusing on "new communication strategies to be able to really target our younger people through social media and streaming services."

"If we have to go door-to-door, we'll go door-to-door," Justice said in a statement.

The FDA, which is currently reviewing data submitted by Pfizer, will have to amend the emergency use authorization for the vaccine, but the process should be straightforward, the official said.