ProQuad is a measles, mumps, rubella and varicella virus vaccine. Measles, mumps, rubella, and varicella are serious diseases caused by viruses. They are spread from person to person through the air. Measles virus can cause minor symptoms such as skin rash, cough, runny nose, eye irritation, or mild fever. It can also cause more serious symptoms such as ear infection, pneumonia, seizures, permanent brain damage, or death. Mumps virus causes fever, headache, and swollen glands, but more serious symptoms include hearing loss, and painful swelling of the testicles or ovaries. Mumps can cause breathing problems or meningitis, and these infections can be fatal. Rubella virus (also called German Measles) causes skin rash, mild fever, and joint pain. Becoming infected with rubella during pregnancy can result in a miscarriage or serious birth defects. Varicella (commonly known as chickenpox) is a common childhood disease that causes fever, skin rash, and a breakout of fluid-filled blisters on the skin. Most people who receive ProQuad will not get chickenpox, or will get only a mild case and will recover faster. Chickenpox is usually mild, but it can be serious or even fatal in young infants and in adults. It can lead to severe skin infection, breathing problems, brain damage, or death. A person who has had chickenpox can develop herpes zoster (also called shingles) later in life, which causes severe nerve pain, and hearing or vision problems, which may last for months or years. Measles, mumps, rubella, and varicella are spread from person to person. ProQuad vaccine is used to help prevent these diseases in children. This vaccine works by exposing your child to a small dose of the virus or a protein from the virus, which causes the body to develop immunity to the disease. ProQuad will not treat an active infection that has already developed in the body. ProQuad is for use in children between the ages of 12 months and 12 years old. Like any vaccine, ProQuad may not provide protection from disease in every person.