Although many vaccines become mandatory for school-aged children about eight years after the CDC's Advisory Committee on Immunization Practices (ACIP) recommends them, the human papillomavirus vaccine has fallen far behind, new research shows. HPV vaccines are only required in two states and Washington, D.C. despite being recommended by the ACIP in 2007. By comparison, the ACIP recommended that all children get the varicella vaccine in 1996. Eight years later, 39 states required children to be vaccinated against the chickenpox before entering public school.