'The Last of Us' finale finally explains why Ellie is immune

As well as beating us over the head with yet another intense volley of emotional punches, The Last of Us finale also answered a key mystery that's been hanging over the show since episode 1: Why, exactly, is Ellie (Bella Ramsey) immune? What makes her unique?

Ellie's past, in general, has been a bit of a mystery since she...