CHICAGO (CBS) — New numbers from the Centers for Disease Control and Prevention show an increasing number of Americans are skipping their second COVID-19 vaccination shots.

Some people cite problems with vaccine providers, while others say they are concerned about side effects.

READ MORE: 1 Killed, 8 Wounded In Weekend Shootings In Chicago

Either way, health experts say it is disturbing.

The CDC said about 8 percent of Americans have missed their second dose, but from 3.4 percent just last month.

However, the agency also said the numbers do not take into account people who get their first dose at one clinic and their second at a different place.

READ MORE: Bo, The Obama Family Dog And 'Best Friend', Dies After Battle With Cancer

Experts said that without that second dose, you are not fully vaccinated and you are still vulnerable.

“This vaccine is our ticket to ride,” said Dr. Mike Saag, Associate Dean of Global Health at the University of Alabama at Birmingham School of Medicine. “This is our ticket to freedom of returning back to normal life.”

We reached out to Chicago area county health departments to see what they have experienced. Lake County north of Chicago said it has a list of people who have not recorded a second shot.

MORE NEWS: Leroy Long Charged With Shooting On Dan Ryan Expressway Near 87th Street

The department is calling them and may send out letters if that doesn’t work.

CBS 2 Chicago Staff