title: Immune response to 13-valent pneumococcal conjugate vaccine with a reduced dosing schedule.
abstract: BACKGROUND
  The 7-valent pneumococcal conjugate vaccine (PCV7) has demonstrated effectiveness against pneumococcal illnesses when administered as 3 infant doses plus a toddler dose (3+1 schedule) or as an abbreviated schedule of 2 infant doses plus a toddler dose (2+1 schedule). The 13-valent pneumococcal conjugate vaccine (PCV13) is approved and World Health Organization-prequalified for administration in a 2+1 schedule when used as part of routine immunization programs.
  
  
  OBJECTIVE
  To summarize immunologic responses elicited by PCV13 administered in a 2+1 schedule and following 2 doses in a 3+1 schedule.
  
  
  METHODS
  Studies were double-blind, randomized, active-controlled, multicenter studies except the Mexico study (open-label, single-arm). In 2+1 studies, PCV13 was administered at 2, 4, and 12 (UK) or 3, 5, and 11 (Italy) months. In 3+1 studies (Spain and Mexico), assessment was made postdose 2 of the primary series (2, 4, and 6 months). The primary immunogenicity endpoint was the proportion of participants achieving serotype-specific antipolysaccharide immunoglobulin (Ig)G concentrations ≥ 0.35μg/mL (i.e., responders) 1 month postdose 2. Pneumococcal IgG geometric mean concentrations (GMCs), opsonophagocytic activity (OPA), and concomitant vaccine responses were assessed.
  
  
  RESULTS
  PCV13 and PCV7 elicited comparable immune responses for the 7 common serotypes after 2 infant doses. The proportion of PCV13 responders postdose 2 was >85% for most of the 7 common and 6 additional serotypes, except common serotypes 6B (27.9-81.4%) and 23F (55.8-77.5%) and additional serotypes 3 (73.8-96.9%) and 6A (79.2-94.4%). Serotypes 6B and 23F elicited lower IgG GMCs postdose 2 compared with other serotypes; all serotypes demonstrated boosting posttoddler dose. All serotypes demonstrated functional activity; >95% of participants achieved OPA levels ≥ 1:8 postdose 2. Concomitant vaccine responses were similar between PCV13 and PCV7 groups.
  
  
  CONCLUSIONS
  Immune responses elicited by PCV13 following 2 infant doses support transition from PCV7 to PCV13 in countries using a 2+1 schedule.
authors: Pfizer Inc, Collegeville, PA, USA. Electronic address: gail.l.rodgers@gmail.com.
authors: Gail L
authors: GL
authors: Rodgers
authors: Susanna
authors: S
authors: Esposito
authors: Nicola
authors: N
authors: Principi
authors: Maricruz
authors: M
authors: Gutierrez-Brito
authors: Javier
authors: J
authors: Diez-Domingo
authors: Andrew J
authors: AJ
authors: Pollard
authors: Matthew D
authors: MD
authors: Snape
authors: Federico
authors: F
authors: Martinón-Torres
authors: William C
authors: WC
authors: Gruber
authors: Scott
authors: S
authors: Patterson
authors: Allison
authors: A
authors: Thompson
authors: Alejandra
authors: A
authors: Gurtman
authors: Peter
authors: P
authors: Paradiso
authors: Daniel A
authors: DA
authors: Scott
mesh_terms: D000907:Antibodies, Bacterial / Q000097:blood; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D007223:Infant; D007558:Italy; D008297:Male; D008800:Mexico; D011008:Pneumococcal Infections / Q000517:prevention & control; D022242:Pneumococcal Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D013030:Spain; D006113:United Kingdom; D014611:Vaccination / Q000379:methods*
chemical_list: C538862:13-valent pneumococcal vaccine; D000907:Antibodies, Bacterial; D007074:Immunoglobulin G; D022242:Pneumococcal Vaccines
keywords: 2+1; Immune response; PCV13; Pediatric; Pneumococcal conjugate vaccine