Trap or not, it would still technically have all sorts of legal repercussions. Sting operations usually are limited to the criminals involved in the sting. In this case, you would be involving innocent US citizens, and knowingly putting them at risk of death and injury. A lot of people would have to be willing to go to prison, or risk execution, if this is some secret antidote.

To create an antidote means you have knowledge the current potions are poison. Therefore, I think it's far more likely if the military had such absolute evidence, they would use their power to halt the administration of the faulty covid potions and then announce to the public an antidote is under development. This would even be politically and visibly preferable over being seen as knowing and allowing a deadly shot being administered while developing the antidote, when they had the power to stop it. I really don't believe this is the case, and if it, it would not be advertised.