Steven Brandenburg told investigators that he had believed the vaccines were microchipped and made recipients infertile.
In a signed plea agreement, he admitted believing in a string of conspiracy theories, which include the Earth being flat and the 9/11 attacked being staged.
And court papers stated that Brandenburg has communicated his beliefs and “notions of alternative history” to his co-workers for at least two years before the incident.
Federal prosecutors charged him with recklessly disregarding the risk posed to another person by tampering with the vaccines, which he removed from cold storage during two shifts.
Brandenburg admitted in court filings that he knew that removing the vaccines from cold storage could make them less effective or dangerous.
In addition to the three year prison term, he will have to serve three years of supervised release.
Prosecutors cited his belief in conspiracy theories as a reason he should be immediately remanded in custody.
But Judge Brett Ludwig disagreed, saying that Brandenburg has no previous criminal history.
Brandenburg’s lawyer told the court that his client had been going through a stressful divorce at the time of the incident.
When initially questioned after the misplaced vials were discovered on 26 December, Brandenburg told officials it was an inadvertent error.
But during a further review he later admitted that he intentionally removing the vaccine from a hospital refrigeration unit.
Moderna told the hospital after the incident that anyone injected with the spoiled vaccine faced no danger, other than not being protected against the virus.
Brandenburg has also been charged in Ozaukee County court with attempted criminal damage to property, to which he has pleaded not guilty.
As part of that case he has surrendered eight firearms to sheriff’s deputies.