Arizona Department of Health Services

The state-run State Farm Stadium vaccination site in Glendale.

More than half of U.S. adults have now had at least one dose of a COVID-19 vaccine, but the rate is lower among Arizonans. And Arizona is slipping in nationwide rankings of state vaccination rates. 

The Centers for Disease Control and Prevention report about 48% of Arizonans 18 and older have had a shot as of Tuesday. That puts Arizona in 33rd place among states. Three weeks ago, the state ranked 28th. 

Demand for vaccines in Arizona also appears to be slowing. The state health department said nearly 30,000 appointments at its vaccine sites were unclaimed as of Monday.

Katherine Davis-Young/KJZZ

Nurse Machrina Leach gives a coronavirus vaccine to Dr. Cara Christ, director of Arizona's Department of Health Services during an event to mark the beginning of the state's vaccination campaign.

Department director Dr. Cara Christ said last week the state is going to work more on messaging to encourage Arizonans to sign up for vaccines. And she said she’s hopeful more Arizonans will feel comfortable getting the shot as it gets distributed to more clinics and doctor’s offices, rather than mass vaccination sites.

“We do know that our medical providers play a large role in people trusting and getting vaccinated," Christ said. 

Experts estimate about 80% of the population would need to be immunized to stop the virus from spreading.

→ Q&AZ: What You Need To Know About Getting The Coronavirus Vaccine In Arizona