Live/oral typhoid vacc. I got sick with the flu yesterday. Need to take 4th & final pill today. Does being sick interfere w/ vaccine's effectiveness?

Flu like symptoms. Flu like symptoms are also side effects of the live oral typhoid vaccine. No interference with vaccine effectiveness.
Somewhat. A healthy immune response is augmented by good health, but you should have an adequate GI immune response unless you are in the middle of a raging gastroenteritis complicating your viral illness. Eat blandly and avoid GI upset as much as you can in you diet.