About 600 people must be revaccinated after a Denver health care provider gave expired doses.

The Colorado Department of Public Health and Environment is recommending that nearly 600 people be revaccinated for COVID-19 after a Denver-based provider administered the vaccine after their use-by date had passed.

Bloom Healthcare administered 585 Moderna vaccines between September 2021 and May 2022 that had passed their use-by dates, state public health officials said in a Monday evening news release.

Bloom Healthcare self-reported the error to the state, and is contacting those affected by phone and email, the news release said.

The state had temporarily barred Bloom from administering and repurposing the COVID-19 vaccine, but was recently reauthorized to approve it, health officials said. The state agency said the state is requiring the company to complete a compliance improvement plan for the COVID-19 vaccine “to ensure similar administration errors do not occur again.”

Most doses of the vaccine given by Bloom are unaffected. Vaccines given after their use-by date may be ineffective, but have no adverse effects, CDPHE said.

“The only risk is that it may not provide protection against COVID-19 in the same way that a fixed dose does, and the efficacy of the administered dose cannot be confirmed,” health officials wrote in the release. wrote in the release.