Pediatr Infect Dis J 2009;28:678-681. & Reuters Health, Aug 12 – During an outbreak of varicella (commonly called chicken pox) in an elementary school in Arkansas, students who were vaccinated once or twice still came down with the illness, though their symptoms were mild. Furthermore, vaccine effectiveness was no better among those who received two inoculations prior to the outbreak than those who received only one. In June 2006, the Advisory Committee on Immunization Practices (ACIP) recommended a second dose of varicella vaccine for children at age of school-entry. Dr. Gould, from the Centers for Disease Control and Prevention in Atlanta, and his team estimated vaccine effectiveness as 85.4% for one dose and 89.1% for two doses.
Varicella zoster virus is a member of the herpesviridae family. Other members include Herpes simplex 1 & 2, cytomegalovirus and Epstein-Barr virus. Like all other herpesviruses, once infected, we harbor the virus for life. Varicella can sometimes come back with a vengeance in our golden years or in an immunosuppressed state (transplant patients or persons infected with HIV) in the form of shingles. This particular vaccine uses a live varicella virus preparation called Oka that has been selected to be a weaken version of its original inoculum. Why did children who got 1 or 2 doses of the vaccine still get chicken pox?
Maybe this is a new strain of varicella that is is stronger than typical zoster or looks a little different to the immune system compared to the Oka vaccine.