Updated: July 16, 2009

Table of Contents

    Understanding the Disease

    Varicella (chickenpox) is an infection caused by the varicella-zoster virus (VZV). The infection usually starts as a rash on the face that spreads to the rest of the body. The rash begins as red bumps that eventually become blisters. A child will often get 300 to 500 blisters during the infection, which crust over and fall off in one to two weeks. The virus can be spread in the fluid from the blisters or droplets from an infected person’s nose or throat.

    Varicella is generally a mild disease, but it is highly contagious and can be severe and even fatal in otherwise healthy children (less than 1 out of every 10,000 cases). Chickenpox can cause pneumonia (23 out of every 10,000 cases), and is an important risk factor for developing severe invasive “strep” (group A streptococcal disease), commonly referred to as “flesh-eating disease.” Treatment of this deep infection requires antibiotics and surgery to remove the infected tissue. Complications of varicella include bacterial infections (up to 5% of cases), decreased platelets, arthritis, hepatitis, and brain inflammation (1 in 10,000 cases), which may cause a failure of muscular coordination. Complications are more common among adolescents and adults, and in immunocompromised persons of all ages, than in children.

    The virus which causes chickenpox remains in the body for life and may reappear as shingles, particularly in the elderly.

    A woman who contracts chickenpox in early pregnancy can pass the virus to her fetus, causing abnormalities in 2% of cases. The fetus can develop scarring of the skin and affected limb(s), limb deformities (hypoplesia), eye damage, low birth weight, brain atrophy, and mental retardation. The virus sometimes leads to fetal demise or spontaneous abortion, while some infected fetuses die in infancy. A pregnant woman who has never had chickenpox, but has been exposed, should contact her physician immediately.

    Prior to the introduction of the varicella vaccine, there were 3 to 4 million cases of varicella in the United States each year. About 10,000 people were hospitalized with complications, and approximately 100 patients died. While only 5% of reported cases of varicella are in adults, adults account for 35% of the deaths from the disease.

    Although national figures demonstrating the decline in varicella are not yet available, smaller-scale studies show that the vaccine is effective in reducing the number and severity of chickenpox cases. A number of studies have demonstrated that varicella-containing vaccines are effective in preventing disease in large populations of students. However, when chickenpox exposure occurs, breakthrough chickenpox (that is chickenpox lesions in an immunized person) can occur. Most children who are immunized but later develop chickenpox have mild disease, although some may have more typical illness with fever and many lesions. Breakthrough varicella can be contagious. As a consequence, in June 2006, the Centers for Disease Control and Prevention recommended a second dose of varicella-containing vaccine for all children.

    In 2005 a combination measles, mumps, rubella, varicella vaccine was licensed.

    Available Vaccines

    Product: Varivax®
    Manufacturer: Merck
    Year Licensed: 1995

    Product: ProQuad® (Measles-Mumps-Rubella-Varicella Virus Vaccine Live, MMRV)
    Manufacturer: Merck
    Year licensed: 2005

    Reconstituted MMRV must be discarded if not used within 30 minutes. CDC recommends storage of all live vaccines (MMR, MMRV and varicella) in the freezer at 5o F or below.

    These vaccines do not contain thimerosal. For information on the thimerosal content in vaccines, see:

    • the Food and Drug Administration at, or
    • Johns Hopkins University’s Institute for Vaccine Safety at

    History of the Vaccine

    A varicella vaccine developed in Japan in the 1970’s was licensed for routine use in Japan and Korea in 1988. The varicella vaccine was recommended for routine use in the United States in 1995. In 2005 a combination measles, mumps, rubella, varicella vaccine (MMRV) was licensed. The risk of a febrile seizure after the first dose of MMRV is increased by an additional child per 1000 (compared to children who got MMR and varicella vaccine at different sites on the same day).

    Who Should and Should Not Receive the Vaccine

    Who should receive the vaccine?

    • All children aged 12 to 18 months
    • All older children and adults who have not had chickenpox and have not been vaccinated or who have had only one dose of chickenpox vaccine.
    • If someone who has never had chickenpox disease or received the vaccine is exposed to chickenpox, giving him or her the vaccine within 72 hours will probably prevent or significantly reduce the severity of the disease. It is recommended under such circumstances.

    Who should not receive the vaccine?

    • People who have had a life-threatening allergic reaction to gelatin, to the antibiotic neomycin, or (for those needing a second dose) to a previous dose of the chickenpox vaccine
    • Those who are receiving the MMR vaccine simultaneously should not get the varicella vaccine from the same needle or in the same place on the body unless it is administered as the manufacturer’s formulation MMRV.
    • Pregnant women should wait until after they give birth to receive the vaccine. Women should not become pregnant for at least one month after receiving the vaccine. To date, there are no reported cases of congenital varicella syndrome caused by the vaccine.
    • Persons with T-lymphocyte immunodeficiency, including those with leukemia, lymphoma, other malignancies affecting the bone marrow and congenital T-cell abnormalities. The vaccine may be given to children with acute lymphocytic leukemia under study conditions, and HIV-infected persons who are immunocompetent may be vaccinated. Susceptible family members and other contacts of HIV-infected or immunodeficient persons should receive the chickenpox vaccine, because of the risk that natural chickenpox and its complications present for these patients.
    • Varicella vaccine should not be given for five months following the receipt of antibody-containing (e.g., blood transfusion) products.
    • People who are moderately or severely ill should consult with their physician before receiving any vaccine.

    This vaccine is recommended by:

    • Advisory Committee on Immunization Practices of the Centers for Disease Control and Prevention
    • American Academy of Pediatrics
    • American Academy of Family Physicians

    The complete childhood immunization schedule can be found at:

    The summary of adolescent/adult immunization recommendations can be found at:

    Dose Schedule

    Children should get two doses of a varicella-containing vaccine: The first dose between 12 and 15 months of age and the second dose between 4 and 6 years of age (before entering kindergarten or first grade).

    People who have not been vaccinated by 13 years of age should get two doses of the vaccine, four to eight weeks apart.

    Note: Because varicella vaccine has been shown to be less effective when given between 1 and 29 days after MMR vaccine, it should either be given on the same day as MMR, or 30 or more days after MMR vaccine is administered.

    Effectiveness of the Vaccine

    Varicella vaccine is 85% to 90% effective for prevention of varicella and 100% effective for prevention of moderate or severe disease.

    Children receiving varicella vaccine in pre-licensure trials in the United States have been shown to be protected for 11 years. Studies in Japan have demonstrated protection for at least 20 years. However, breakthrough infection (i.e., cases of chickenpox after vaccination) can occur in some who have been immunized. Although breakthrough varicella usually results in mild rather than severe illness, some school outbreaks have resulted in some children with more lesions and them also being contagious. For this reason, a second dose of a varicella-containing vaccine is recommended.

    For more recent studies on the effectiveness of the varicella vaccine, see Immunization Science: Varicella (chickenpox) vaccine.

    Known Side Effects

    A majority of people who get the vaccine have no side effects. Of those who do have side effects, most will have only a mild reaction such as soreness and swelling where the shot was administered, and a mild rash. Pain and redness at the injection site occurs in about one in five children (and about 1 in 3 teenagers). About one in five may have a also few chickenpox-like lesions at the injection site.

    One to three weeks after vaccination, some may develop a few chickenpox-like lesions elsewhere on their bodies.

    Although fever occurs in as many as fifteen percent of children following varicella vaccine it also occurred in children who had received the placebo instead of vaccine.

    MMRV combination vaccine has comparable rates of reactions to children who received MMR and varicella vaccine at different sites—except that those that received MMRV vaccine more commonly experienced fever, a measles-like rash and rash at the injection site. It has also been observed that children who received MMRV vaccine had an increased risk of febrile seizures of about one child per 1000 when compared to children who got MMR and varicella vaccine at different sites on the same day.

    Related Issues

    Confusion about vaccine safety and concerns about potential side effects of vaccines have led some parents to consider not immunizing their children. A few have even sought out other parents to help each other’s children catch diseases (such as chickenpox and measles) in what is called “exposure parties”.

    Before vaccine became available, “chickenpox parties” were considered a way to get a child protected from serious chickenpox at an age when the infection is ordinarily less severe. See NNii’s article on the risks of chickenpox parties.

    Key References and Sources of Additional Information

    CDC Information