I can't finish Strangerville

No matter what I do (repair the game several times, resetted the files several times, have my Sim "fast travel" to other places to see if it would cancel effects, reset him or other Sims around etc), I am stuck at the vaccine part. My Sim would throw it to a selected Sim, then both would just freeze with no more interaction, time passing by, people around passing by. There also was a variant that falsely gave me hope in which the vaccine did work, but mid conversation the 2 froze. 2 weeks this has happened and that I can't finish that story, I'm getting tired of this. I have mods, but I kept reading everywhere mods have nothing to do. Please, somebody help, it's frustrating and taking away all the fun!