The Aurora statement notes that they have contacted authorities. As the Milwaukee Journal reports, the Grafton Police Department issued their own statement on Wednesday evening that it was investigating “an employee tampering with vials of the COVID-19 vaccine.” The police in turn contacted both the FBI and FDA, both of which have joined the investigation.
It remains unclear why the now fired employee took such an action. It might have been a general anti-vaccine action, it could have come from the delusion that COVID-19 is somehow less dangerous than the vaccine, or it might have been some more elaborate fantasy, like the Q-Anon connected claims that former Microsoft CEO Bill Gates is adding “microchips” to the vaccine.
Police indicate they believe this was the act of just one person. Considering the state of the pandemic, and the problems with the vaccine rollout, it can only be hoped this is the only such act.