When you are escaping the sewers with Henry and his brother, there are clickers and other enemies coming through a double door. Well, I've set those enemies on fire, shot point blank with a shotgun, shived them in the back, and punched them dozens of times yet they are unharmed. They dont even set nail mines off, however they can kill you or Ellie. Restarting or reloading the game hasn't fixed anything, so help fixing this evident bug is much appreciated.
You can’t kill the infected at this stage. You have to unlock the gated door to your right and flee.