A health worker in Wisconsin has been sacked after deliberately spoiling 500 doses of a coronavirus vaccine.

Police, the FBI and the US Drug Administration are all investigating after the worker removed the doses from where they were being refrigerated at the Aurora Medical Center on the outskirts of Milwaukee.

Detectives said they had been told about the tampering on Wednesday evening. As of Thursday there had been no arrests.

In a statement, the Aurora centre said the employee involved had "acknowledged that they had intentionally removed the vaccine from refrigeration".

The statement made no mention of a motive.

It said: "We continue to believe that vaccination is our way out of the pandemic. We are more than disappointed that this individual's actions will result in a delay of more than 500 people receiving their vaccine."

The number of coronavirus cases in Wisconsin is on the rise, following a brief slowdown at the start of December.

Johns Hopkins University states that there have been 516,226 total cases of the virus in the state, with 5,192 deaths.

Around 47,157 people have been vaccinated in Wisconsin, out of a total population of around 5.8million.