A US pharmacist is in custody accused of deliberately ruining hundreds of doses of coronavirus vaccine by removing them from refrigeration for two nights.

The Grafton Police Department in Milwaukee, Wisconsin, said the former Advocate Aurora Health pharmacist was arrested on suspicion of reckless endangerment, adulterating a prescription drug and criminal damage to property.

His motive remains unclear. Police said that detectives believe he knew the spoiled doses would be useless and people who received them would mistakenly think they had been vaccinated when they had not.

Advocate Aurora Health chief medical group officer Jeff Bahr told reporters the pharmacist deliberately removed 57 vials that held hundreds of doses of the Moderna vaccine from refrigeration at a Grafton medical centre overnight on 24 December.