What it prevents:
Measles: This highly contagious virus (it’s spread through coughing or sneezing) causes a cough, runny nose, fever and conjunctivitis, and can also lead to pneumonia and croup. One in 1,000 cases are severe enough to infect the brain, causing permanent damage and even death. There have been dangerous outbreaks of measles recently in the United States, nearly all of them in children who had not been vaccinated.
Mumps: Another highly contagious virus (also spread through coughing and sneezing), mumps causes swelling of the salivary glands. One in 2,000 cases is severe enough to cause permanent deafness.
Rubella: Also known as German measles, rubella is a highly contagious virus (again spread by coughing and sneezing) that causes swelling of the lymph nodes in the neck. In severe cases rubella can cause an infection of the brain or joint pain. Rubella poses the greatest threat to pregnant women because it can cause major birth defects in the fetus, including deafness, blindness, mental retardation and heart defects. Known as congenital rubella syndrome, this condition can also lead to a miscarriage, especially if the mom is infected in her first trimester.
When it’s given: The vaccine is given in two doses: one between 12 and 15 months, and the second between four and six years. The MMR vaccine can be given as a single shot or as part of a combination shot together with the Varicella (Chicken Pox) vaccine (known together as MMRV).
What you may have heard: Many of parents’ fears about vaccines surround the MMR shot. No doubt if you’ve ever googled vaccines, you’ve heard the claims by some that the MMR (or the preservative thimerosal that it used to contain) causes autism, a spectrum of behavioral disorders, rates of which have increased in recent years. This claim persists despite the fact the original research that supported this link (a study of 12 children published in the British Medical Journal The Lancet in 1998) has been retracted by nearly all its authors; The Lancet itself has also retracted it for major ethical violations. Since this research, more than ten studies have examined this link and none have found any connection. The Institute of Medicine, the World Health Organization, and the American Academy of Pediatrics have all stated that the MMR vaccine and thimerosol are not linked to autism. “The possible link between vaccines and autism has been taken very seriously,” says Anne Schuchat, director of the National Immunizations Program at the U.S. Centers for Disease Control and Prevention (CDC). “But at this point, after so many studies, it’s safe to say these two hypotheses have been eliminated as possible causes.”
Risk of a reaction: More than 80 percent of children receiving the shot will not have a reaction. Here are the risks and ranges of reactions, according to the CDC. The risk of contracting measles, mumps, or rubella is far greater than the risk of any of the reactions.
Mild: 1 in 6 will have a fever; 1 in 20 will have a rash; very rarely, swelling of the glands can occur.
Moderate: 1 in 3,000 may have a febrile seizure (a harmless fever-related seizure that nonetheless is scary for parents); 1 in 30,000 may have a temporary low platelet count. Note that the first dose of the combination shot (MMRV: MMR with Varicella) is associated with a higher risk of rash (1 in 20) and fever (1 in 5). The rate of febrile seizures is also slightly higher for children who receive the MMRV shot.
Severe: 1 in a million may have a serious allergic reaction. Even more rare are conditions that may or may not be associated with the vaccine – deafness, long-term seizures, and permanent brain damage.
Allergy info: MMR should not be given to a child who has had a life-threatening allergic reaction to gelatin, the antibiotic neomycin, or to a previous dose of MMR. If you have a family history of allergies, be sure to mention it to your doctor.
Get the lowdown on the best kid and baby thermometers from moms who've battled high fevers—and won
An in-depth look at airborne irritants, contact dermatitis, food allergies and more
14 celebs sound off on the vaccine debate
From cradle cap to scarlet fever -- a field guide to common childhood rashes