In 1978, VZIG prepared from the plasma of normal volunteers identified by routine screening to contain high antibody titers to VZV became available. Administration of VZIG to exposed individuals may prevent or reduce the intensity of disease. A carefully documented history of chickenpox is a primary consideration when determining whether a person is immune to varicella. The type and duration of exposure also will determine the risk of acquiring disease. Patients who are exposed continuously to family members who have disease are at the greatest risk. VZIG is of maximum benefit when administered as soon as possible after the presumed exposure, but it remains effective if given as late as 96 hours after exposure.
The live attenuated varicella vaccine was attenuated by propagation in human embryonic lung fibroblasts, guinea pig embryonic cells, and finally in two different cell lines of human diploid cell cultures. The varicella vaccine has been tested extensively in the United States since 1981, and several formulations have been administered to nearly 10,000 healthy children and 2,000 healthy adolescents and adults.
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Serologic responses to the varicella vaccine have been brisk. Using a sensitive glycoprotein enzyme-linked immunosorbent assay, seroconversion rates of more than 95% have been documented in children 12 months to 12 years of age. Although pre-existing antibody did not appear to decrease the rate of seroresponse to vaccine, responses were not as strong as those seen with natural infection. Immunogenicity of the vaccine was lower in adolescents and adults, with seroconversion rates of 79% to 82% after one dose and 94% after two doses. Persistence of antibody was noted in children in the United States followed for 6 years. In serologic studies conducted in vaccinees in Japan and in the United States, antibodies to varicella were detected for up to 10 years after vaccination in more than 95% of those immunized.
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The vaccine has proven to be effective in clinical trials for more than 10 years. Although breakthrough infections occur in some vaccinated persons, the disease is usually mild. Vaccine efficacy was evaluated in a double-blind randomized, placebo-controlled trial of children 1 to 14 years of age. Efficacy was 100% during the first year after vaccination and 96% after the second season. Vaccine efficacy was estimated to be 95% after 7 years. Protection against any disease in vaccinees after household exposure was approximately 70%, but it was greater than 95% against more severe disease.