Do chickens need injections for any reason?

Yes, not all chickens get injections however but they are often given an injection soon after hatching to help prevent a specific disease called Marek's disease. The preventative medicine for this can also be given via water soluble dosage and is often used on small hobby farms rather than injectable solutions. Much of the medicine a chicken will need can be added to their water supply.

Chicks shipped from major hatcheries will have had an injection for this disease.