An MMR vaccination is necessary for your child as it protects against three deadly viral infections mumps measles and rubella. Mumps is a contagious disease caused by a virus that passes from one person to another through saliva nasal secretions and close personal contact. The condition primarily affects the salivary glands also called the parotid glands with severe pain and swelling. A measles infection on the other hand is accompanied with high fever rash across the body cough running nose and red watery eyes. The infection weakens one s immune system and leads to serious complications that include blindness encephalitis