title: Immunogenicity of Oka/Merck varicella vaccine in children vaccinated at 12-14 months of age versus 15-23 months of age.
abstract: OBJECTIVE
  Recent reports suggest that breakthrough varicella may be more common in children when the Oka/Merck varicella vaccine is given at 12-14 months of age than when it is given at older ages. An analysis of 5 postlicensure clinical trials with this vaccine was conducted to evaluate immune response relative to the age of the vaccine recipient.
  
  
  METHODS
  In 5 clinical trials, 3771 children, 12 through 23 months of age with no history of varicella, received an injection of varicella vaccine. Varicella-zoster virus (VZV) antibody was measured 6 weeks postvaccination by glycoprotein enzyme-linked immunosorbent assay (gpELISA), an assay that correlates with neutralizing antibody. Endpoints evaluated were the response rate (percent of subjects with VZV antibody > or =5 gpELISA units/mL, a titer shown to correlate with protection) and geometric mean titer (GMT) of VZV antibody. Each endpoint was compared across 3 age groups (12-14, 15-17, and 18-23 months of age). Response rates by initial VZV serostatus were evaluated for children vaccinated at 12-14 months of age to assess whether maternal antibody had an impact on the immune response.
  
  
  RESULTS
  The response rates were similar among 12-14, 15-17, and 18-23 month olds (93.8, 90.8, and 93.1%, respectively); GMTs were significantly higher among the 12-14 month olds (15.1, 13.5, and 13.7 gpELISA units/mL, respectively). Among children 12-14 months of age, response rates and GMTs were similar regardless of their prevaccination VZV serostatus.
  
  
  CONCLUSIONS
  Oka/Merck varicella vaccine is highly immunogenic when given to children 12-14 months of age. The immunogenicity profile is similar to that of children 15-17 and 18-23 months of age. The presence of low titers of VZV antibody before vaccination did not influence vaccine response in 12-14 month olds. These results support current recommendations for universal varicella vaccination beginning at 12 months of age.
authors.affiliation: Merck & Co., Inc., West Point, PA 19486, USA.
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Silber
authors.forename: Ivan S F
authors.initials: IS
authors.lastname: Chan
authors.forename: William W
authors.initials: WW
authors.lastname: Wang
authors.forename: Holly
authors.initials: H
authors.lastname: Matthews
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: Kuter
mesh_terms: D000375:Aging / Q000276:immunology*; D000914:Antibodies, Viral / Q000097:blood / Q000276:immunology; D002644:Chickenpox / Q000276:immunology* / Q000517:prevention & control*; D019433:Chickenpox Vaccine / Q000008:administration & dosage* / Q000276:immunology*; D004334:Drug Administration Schedule; D014645:Herpesvirus 3, Human / Q000276:immunology; D006801:Humans; D007223:Infant
chemical_list: D000914:Antibodies, Viral; D019433:Chickenpox Vaccine