Varicella Immunization

Varicella vaccine is a live-virus vaccine. It has been used in some parts of the world, such as Japan, for over 20 years. It was licensed in the United States in 1995.

A single dose of varicella vaccine is recommended for children between 12 and 18 months of age. It is usually given at the same time as the MMR shot. Children who miss this shot can still get a single dose of the vaccine up to their 13th birthday. Adolescents or adults who haven't gotten the vaccine by their 13th birthday will need two doses, 4 to 8 weeks apart. A child who has already had chickenpox disease does not need to get the shot.

It appears that the vaccine prevents chickenpox in about 70% to 90% of people who get the shot, and prevents severe chickenpox in over 95%. The vaccine used in Japan is still protecting those people who were vaccinated 20 years ago. In the United States, people who were vaccinated during testing, before the vaccine was licensed, are still immune to chickenpox. The vaccine is expected to give lifelong immunity.

Occasionally even children who respond to the vaccine get a very mild case of chickenpox (about 1-2 children out of a hundred).

There is some concern that a child who gets chickenpox vaccine can actually give chickenpox to other, unprotected, family members. This appears to happen extremely rarely, and only when the child who was vaccinated develops a rash. To be safe, anyone with a suppressed immune system should consider avoiding contact with a child who develops a rash after getting the chickenpox vaccination, just as they should avoid anyone who has a case of chickenpox.

Side Effects from Varicella Immunization
Varicella vaccine is very safe. Some children (about 1 out of 5) get red or sore where the shot was given. Some children also get a mild rash (about 5 spots), about 1 to 3 weeks after the shot. Febrile seizures (seizures caused by fever) have occurred in less than 1 out of a thousand children; and other serious problems, such as inflammation of the brain (encephalitis) or loss of muscle coordination, have been reported very rarely. These problems happen so rarely that experts cannot tell whether or not they are caused by the vaccine, or just happen at the same time by chance.

Like any vaccine, or medicine, varicella vaccine could theoretically trigger a serious reaction in someone who is allergic to one of its components. But severe allergic reactions to childhood vaccines are very rare (estimated at around one per million doses), and no child is ever known to have died from an allergic reaction to a vaccine.

Precautions
There are several reasons a doctor might want to delay giving a child a varicella vaccination or not give it at all:

• A child who is known to have a severe allergy to gelatin or the antibiotic neomycin should not get varicella vaccine.
  
• A child who had a life-threatening allergic reaction after a dose of varicella vaccine should not get another dose.
  
• A child with a suppressed immune system (because of a disease such as cancer or HIV
  infection, or medication such as steroids) should be evaluated by a doctor before getting varicella vaccine.
  
• A child who has recently gotten a transfusion or other blood product might have to wait several months before getting varicella vaccine.
  
• A child who has a moderate or severe illness on the day a varicella (or any) vaccination is scheduled should probably delay the vaccination until he or she has recovered.

After Getting Varicella Vaccine . . .
If the child has any serious or unusual problem after getting this vaccine, call a doctor or get the child to a doctor right away.

U.S. DEPARTMENT OF HEALTH & HUMAN SERVICES
Centers for Disease Control and Prevention
National Center for Immunization and Respiratory Diseases