Immunogenicity and boosting after a reduced number of doses of a pneumococcal conjugate vaccine in infants and toddlers.
BACKGROUND
The minimum number of doses of pneumococcal conjugate vaccine required for protection is not known. We studied the immunogenicity of a reduced schedule in infants and toddlers.


METHODS
U.K. infants were given either 2 or 3 doses (at 2 and 4 or 2/3/4 months of age) of a 9-valent pneumococcal conjugate vaccine (9VPCV) followed by boosting at 12 months of age. In a separate study, toddlers (12 months) received 1 or 2 doses (2 months apart) of 9VPCV followed by pneumococcal polysaccharide vaccine at 18 months of age.


RESULTS
For infants, serotype-specific IgG geometric mean concentrations were similar post-primary immunization between the groups with both showing avidity maturation and similar booster responses. For toddlers, the primary response to 4 of the 9 serotypes was lower in the 1- compared with the 2-dose group (type 6B, 0.77 versus 7.1; type 14, 4.67 versus 14.98; type 19F, 5.05 versus 7.75; type 23F, 2.48 versus 5.05), although for all serotypes booster responses were similar between groups, and the postprimary responses in the 1-dose group were at least as high as those after infant immunization.


CONCLUSIONS
The 2-dose infant priming schedule of 9VPCV is comparable with the 3-dose schedule and may thus be equally protective, whereas 1 dose in toddlers may suffice for a catch-up.
Institute of Child Health, University College London, UK. d.goldblatt@ich.ucl.ac.uk
David
D
Goldblatt
Jo
J
Southern
Lindsey
L
Ashton
Peter
P
Richmond
Polly
P
Burbidge
Juliana
J
Tasevska
Annette
A
Crowley-Luke
Nick
N
Andrews
Rhonwen
R
Morris
Ray
R
Borrow
Keith
K
Cartwright
Elizabeth
E
Miller
D000907:Antibodies, Bacterial / Q000097:blood; D004306:Dose-Response Relationship, Immunologic; D006801:Humans; D007115:Immunization Schedule; D007117:Immunization, Secondary; D007074:Immunoglobulin G / Q000097:blood*; D007223:Infant; D011008:Pneumococcal Infections / Q000517:prevention & control; D022242:Pneumococcal Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification / Q000276:immunology; D018074:Vaccines, Conjugate / Q000008:administration & dosage* / Q000276:immunology*
D000907:Antibodies, Bacterial; D007074:Immunoglobulin G; D022242:Pneumococcal Vaccines; D018074:Vaccines, Conjugate