Chickenpox (varicella) is a common contagious illness caused by a type of herpes virus. You can prevent chickenpox by getting the varicella-zoster vaccine(What is a PDF document?), commonly called the chickenpox vaccine. The vaccine is recommended for:

• All healthy children 12 months of age and older who have not had chickenpox. It is given in 2 doses: the first at 12 to 15 months and the second at 4 to 6 years. (The second dose may be given earlier if it's been at least 3 months since the first dose.) The vaccine can also be given in a single shot that also contains the vaccines for measles, mumps, and rubella. This combination shot is known as MMRV (ProQuad) and can be substituted for one or both of the regular measles, mumps, and rubella (MMR) shots. (Immunization with MMR combination vaccine is recommended for children between 12 to 15 months of age and again at 4 to 6 years of age.)
• Children who have completed their routine immunizations but have not had chickenpox. Many states now require that children entering day care and school have the vaccine unless they show proof of immunity (doctor's diagnosis or blood test results).
• Teens and adults who have not had chickenpox.
• People who do not know whether they had chickenpox as a child. It is safe for them to receive the chickenpox vaccine even if they had chickenpox in the past.
• People who have not had chickenpox or the vaccine and have been exposed to someone ill from the virus.

Most health organizations recommend the chickenpox vaccine. It provides about 95% protection from moderate or severe infection and 70% to 85% protection against mild infection.² Occasionally people who receive the vaccine develop what is called breakthrough infection. This may occur when they are exposed to a "wild-type" chickenpox virus. But in these cases, the infection is mild, with fewer blisters and symptoms than the usual chickenpox infection. Talk with your health professional if you have questions or concerns about the vaccine. For more information on routine immunizations, see the topic Immunizations.

Some research indicates that the chance of developing a breakthrough chickenpox infection after vaccination increases with the length of time since vaccination.^{3, 4} In one study, the effectiveness of the vaccine declined after the first year when given to children younger than 15 months.⁵ As a result of these studies, experts are debating whether a second vaccination, or booster, should be recommended for children younger than 13.

You also can prevent chickenpox by having a shot of chickenpox antibodies soon after exposure to the virus. If you have been in contact with a person who has chickenpox and are not sure whether you are immune, talk with your health professional about whether you should have either the chickenpox vaccine or antibodies.