MADISON (REUTERS) - A Wisconsin pharmacist has agreed to plead guilty to purposely trying to spoil hundreds of doses of Moderna's Covid-19 vaccine in a bid to render them ineffective, the US Justice Department said.

Steven Brandenburg, 46, is charged with two counts of attempting to tamper with consumer products and with reckless disregard for the risk that another person will be placed in danger of death or bodily injury, according to the statement by the Justice Department.

It said he believed in various "conspiracy theories" and was sceptical of vaccines in general and specifically the vaccine by Moderna.

The US Food and Drug Administration has deemed Moderna's vaccine safe and effective.

Brandenburg has signed a plea agreement to plead guilty to the charges, which each carry a maximum sentence of 10 years' imprisonment, the statement added.

In late December, he intentionally removed a box of Covid-19 vaccines on two successive night shifts from a refrigerator in Aurora Medical Centre in Grafton, Wisconsin, so that he could ruin their effectiveness, according to the statement.

He left them out for several hours before placing them back in the refrigerator to be used by the clinic the next day, the statement said, adding that 57 people had already received doses of the vaccine from those vials before his conduct was discovered.

Moderna's vaccine has to be stored and shipped frozen, but does not require ultra-cold temperatures and can be stored for 30 days in standard-temperature refrigerators.