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The varicella virus vaccine Varivax (Merck) comes from the Oka/Merck strain of live, attenuated virus. The original virus was obtained from a child with natural varicella.
According to the package insert, the varicella vaccine should not be given to anyone with known hypersensitivity to any of its components, including gelatin and neomycin.1 It is further contraindicated in individuals with blood dyscrasia, leukemia, lymphomas of any type, and other malignant neoplasms affecting bone marrow or lymphatic systems.
Patients on concomitant immunosuppressive therapy and those with primary and acquired immunodeficiency states should not be given the vaccine. Additionally, those with active untreated tuberculosis or any febrile respiratory illness or infection should not be administered the vaccine.
Varivax is contraindicated in pregnant women; caution should be exercised when giving the vaccine to women who are lactating. Women are advised to avoid pregnancy for three months after vaccination, the Merck package insert notes.
The duration of immunity is currently unknown, and thus guidelines for boosters are undetermined, Merck says. However, elevated antibody titers have been observed in several vaccinated persons following exposure to wild-type varicella and following a booster of varicella vaccine four to six years after initial vaccination. In a population that is highly vaccinated against varicella virus, lack of exposure to the virus may cause immunity to wane. Postmarketing surveillance continues to evaluate the potential need for and timing of booster doses.
Patients should avoid use of salicylates after vaccination for a period of six weeks as Reye's syndrome has been reported following the use of salicylates during the natural course of varicella, the package insert notes.
In clinical trials, adverse events reported at a significantly greater rate in vaccinated subjects than in placebo subjects were pain and redness at the site of injection, Merck reports.
1. Varivax [package insert]. West Point, PA: Merck & Co; 1995.