The Advisory Committee on Immunization Practices (ACIP) to the Centers for Disease Control and Prevention (CDC), in its meeting in
Fifteen to 20 percent of children who have received one dose of the vaccine are not fully protected and may develop chickenpox after coming in contact with varicella zoster virus. Additionally, one dose of the vaccine may not continue to provide protection into adulthood when chickenpox is more severe. A second dose of varicella vaccine provides increased protection against varicella disease compared to one-dose. The ACIP also recommended that children, adolescents and adults who previously received one dose should receive a second dose.
"We have made great progress in reducing chickenpox during the past ten years," said Dr. Anne Schuchat, director of CDC's
Before licensure of the varicella vaccine in 1995, each year there were about 4 million cases of varicella, 13,500 hospitalizations and 150 deaths. Cases of varicella have steadily declined 80 to 85 percent in surveillance sites since the licensure. From 1995 to 2001, varicella hospitalizations declined by 72 percent and deaths, among those 50 years old and younger, decreased by 75 percent or more.
However, in recent years varicella outbreaks have continued to occur among vaccinated school children. During these chickenpox outbreaks, between 11 and 17 percent of vaccinated children developed varicella. Varicella in vaccinated children is usually mild, but the children are contagious and can transmit the virus to others including their parents who are at higher risk of severe disease.
The ACIP, consisting of 15 members appointed by the Secretary of the Department of Health and Human Services (HHS), advises the director of CDC and Secretary of HHS on control of vaccine-preventable disease and vaccine usage. Recommendations of the ACIP become CDC policy when they are accepted by the director of CDC and are published in CDC's Morbidity and Mortality Weekly Report (MMWR). There are no federal laws requiring the immunization of children. All school and daycare entry laws are state laws and vary from state to state.