As more Americans get their COVID-19 vaccine booster shots, a pharmacy chain says some booster appointments have been cancelled in Maine because of staffing issues.

According to reporting in Bloomberg, Maine CDC Director Dr. Nirav Shah reached out to Walgreens after Mainers took to Twitter to raise concerns about appointments being cancelled.

Shah says a Walgreens spokesperson told him the cancellations were not due to a lack of vaccine supply, but staffing shortages. They said that some pharmacies had adjusted their hours as a result, adding that pharmacies will reach out to people whose appointments have been impacted.