Doctors do not administer vaccinations to people who are too sick. Which best explains why?

The weakened or dead form of the pathogen may be attacked by ther person's immune system.
The weakened or dead form of the pathogen may have a fatal effect when it is combined with medication that the sick people are taking.
The digestive systems of sick people may be negatively affected by the weakened or dead pathogen.
The white blood cells of sick people may not be able to efficiently handle the weakened or dead form of the pathogen.