The unexpected effect is that the vaccine, made to help fight off a type of bacteria, also helps against a virus. So it was a better result than expected.
It's the same immune system that fights those off, too. There are many vaccines for bacterial infections, like cholera and typhoid. Intracellular bacteria don't have many vaccines, but they exist too. I'm no doc though so if you want to know more, it'd be worth a search.