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Varivax "Varicella Virus Vaccine Live" (Merck) is a preparation of the Oka/Merck strain of the live, attenuated (weakened) varicella virus and is indicated for vaccination against varicella (chickenpox) in individuals 12 months of age and older. The duration of protection of Varivax is unknown, however, long-term studies have demonstrated continued protection up to 10 years after vaccination.

The U.S. Centers for Disease Control and Prevention (CDC) recommends that children who have never had chickenpox should receive 2 doses of vaccine according to the following schedule:

• First dose at 12-15 months of age
• Second dose at 4-6 year of age (may be given earlier, if at least 3 months after the first dose)
• Persons 13 years of age and older (who have never had chickenpox or received chickenpox vaccine) should get two doses at least 28 days apart.

The CDC also recommends immunization of asymptomatic children infected with HIV, provided that their CD4 percentage is more than 25%. Two doses of vaccine are given to HIV-infected children, 3 months apart.

Contraindications to the Varivax vaccine include:

• Allergy to any component of the vaccine, including gelatin
• A history of severe allergy (anaphylactic) reaction to neomycin
• Individuals with blood dyscrasias, leukemia, lymphomas of any type, or other malignant neoplasms affecting the bone marrow or lymphatic systems
• Individuals receiving immunosuppressive therapy
• Individuals with primary and acquired immunodeficiency states, including those who are immunosuppressed in association with AIDS
• A family history of congenital or hereditary immunodeficiency, unless the immune competence of the potential vaccine recipient is demonstrated
• Active untreated tuberculosis
• Any respiratory or other active infection associated with a fever
• Pregnancy - the possible effects of the vaccine on fetal development are unknown at this time. Pregnancy should be avoided for three months following vaccination

Guidelines in North America recommend protecting varicella-zoster virus-susceptible immunocompromised patients, including those being treated for leukemia, by immunizing their healthy susceptible contacts. These include healthy children whose pregnant mothers are susceptible to varicella and children whose varicella-zoster virus-susceptible siblings have malignant diseases for which they are being treated.

The most common side effect of the varicella vaccine is rash. Very rare cases of seizures, brain infection (encephalitis), pneumonia, loss of balance (ataxia), and severe allergic reactions have occurred (in approximately 1 out of every 50,000 doses given).

If possible, vaccine recipients should avoid using salicylates (i.e., aspirin) for 6 weeks after receiving varicella virus vaccine due to risk of Reye syndrome.

Varivax may be given along with measles-mumps-rubella (MMR) vaccine in a combination vaccine called MMRV.