AUGUSTA, Maine (AP) Mainers have begun receiving the second dose of the COVID-19 vaccine, the Maine Center for Disease Control and Prevention reports.

It was a small number — only about 18 on Monday — but numbers will grow as the state aims to complete the initial rollout of vaccines by next month, the Maine CDC said.

Dr. Nirav Shah, director of the Maine CDC said the rollout for the vaccination plan has been slower than expected, calling the nation “supply constrained.”

As the state moves forward, it’s considering changing its vaccination plan as it expands from health care workers to essential workers and people older than 75.

State officials are discussing whether to prioritize older residents in that group in the next phase of the rollout. No decisions have been made.