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Vaccine Information

Varicella (Chickenpox)

Entry last updated: May 28, 2004

- Understanding the Disease
- Available Vaccines
- History of the Vaccine
- Who Should and Should Not Receive the Vaccine
- Dose Schedule
- Effectiveness of the Vaccine
- Known Side Effects
- Related Issues
- Key References and Sources of Additional Information
- State Vaccine Requirements
- Important Facts for Parents to Know
- Frequently Asked Questions
- CDC Vaccine Information Statement

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, 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 women 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 approval of the 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 five-year study in Antelope Valley, CA, found that the incidence of varicella fell from 2,934 cases per year in 1995 to 587 cases in 1999, due to increased voluntary vaccination rates in the area (Peterson 2001).

Available Vaccines

Product: Varivax®
Manufacturer: Merck
Year Licensed: 1995

For information on the thimerosal content in this vaccine, see the Food and Drug Administration at www.fda.gov/cber/vaccine/thimerosal.htm#t3
or Johns Hopkins University's Institute for Vaccine Safety at
www.vaccinesafety.edu/thi-table.htm

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. 

Who Should and Should Not Receive this 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
  • 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.
  • 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:
www.cdc.gov/nip/recs/child-schedule.PDF

The summary of adolescent/adult immunization recommendations can be found at: www.cdc.gov/nip/recs/adult-schedule.pdf

Dose Schedule

Children should get one dose of the varicella vaccine between 12 and 18 months of age, or at any age after that if they have never had chickenpox or received the vaccine. Children who have never had the chickenpox should receive the vaccine by age 13 because of the increasing severity of the disease in older adolescents and adults.

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 less than 1% to 4% of those immunized, usually resulting in mild rather than severe illness.

A three-year study completed in November 2000 concluded that the vaccine prevented chickenpox entirely in 85% of the children who received it and protected against moderately severe to severe disease in 97% of children. In other words, the small percentage of immunized children who later developed chickenpox generally had only a mild case of the disease. Scientists also found that the older the children were when vaccinated, the better the vaccine protected them against chickenpox (Vazquez et al. 2001). Researchers cannot yet confirm the immunity is due solely to the vaccine, as exposure to wild-type varicella-zoster virus (i.e., being with other kids infected with chickenpox) can naturally boost immunity even though the exposed child may not get sick. Ongoing studies are being done to track the vaccine’s long-term effectiveness.

Another study of day care and preschool children showed that even when relatively low percentages of children are immunized, chickenpox cases in unimmunized children can decrease substantially. Scientists hypothesize that even though this “herd immunity” helps protect unimmunized people in their childhood, it puts them at higher risk later in life by delaying the possibility of chickenpox infection until adulthood, when serious illness and complications are more common (Taylor 2001).

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.

In very rare cases (far less than 1 child out of 10,000 vaccinated or 0.02% of cases), children have a serious reaction that can include seizures caused by high fever.

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

Also see our image gallery of diseases.

Including available vaccines, history of the vaccine, who should and should not receive it, dose schedules, effectiveness, known side effects, and related issues.


Varicella Vaccine State Requirements

Check to see if your state requires this vaccine.


Important Facts for Parents to Know about the Varicella Vaccine

A fact sheet that gives basic information on this disease, as well as the effectiveness and possible side effects of the vaccine that can prevent it.


Frequently Asked Questions about the Varicella Vaccine

A fact sheet with in-depth answers to common questions about this vaccine.


CDC Vaccine Information Statement for Varicella

Information provided by the Centers for Disease Control and Prevention on specific vaccines and the diseases they can prevent. Healthcare providers are required to give these to their patients before administering a vaccine.

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