Fifth vaccination with dipthteria, tetanus and acellular pertussis is beneficial in four- to six-year-olds.
OBJECTIVE
Diphtheria, tetanus and pertussis serum antibody titers were assessed before a fifth dose of diphtheria-tetanus-acellular pertussis (DTaP) or diphtheria-tetanus-whole cell pertussis (DTwP) vaccination at age 4 to 6 years.


METHODS
Healthy children who had participated in a series of National Institutes of Health-sponsored trials assessing DTwP and DTaP vaccines provided prevaccination sera before a fifth dose of DTwP or DTaP. The trial design was prospective, randomized and double blind. Diphtheria, tetanus and pertussis antibody titers were measured by enzyme-linked immunosorbent assay. Pertussis results are expressed in enzyme-linked immunosorbent assay units/ml based on US Food and Drug Administration reference sera. Tetanus and diphtheria toxin concentrations are expressed in IU/ml with a WHO international reference sera as a standard.


RESULTS
For diphtheria 100% of the children had antibody titers above the minimum protective level of 0.01 IU/ml and 86 to 100% (depending on prior vaccine product) had titers >0.1 IU/ml. However, only 0 to 40% of the children had antibody titers > or =1.0 IU/ml, a titer associated with more certain durable protection. For tetanus none of the children had an antibody titer below 0.01 IU/ml, and 93 to 100% had titers > or =0.1 IU/ml, a titer associated with more certain, durable protection. For pertussis the geometric mean concentrations of antibody before booster were uniformly very low, and the percentage of children exceeding the minimum detectable titer of antibody by 4-fold was also low.


CONCLUSIONS
Before a 4- to 6-year-old booster, a large proportion of children have titers of antibody to diphtheria below the certain, durable protective level. Because serologic correlates and minimum protective titers of antibody to pertussis antigens have not been established, the relevance of the low titers determined in the current study is unknown but a potential concern.
Pichichero
M E
ME
Department of Microbiology and Immunology, University of Rochester School of Medicine, NY 14642, USA. mepo@uhura.cc.rochester.edu
Anderson
E L
EL
Rennels
M B
MB
Edwards
K M
KM
England
J A
JA
D000907:Antibodies, Bacterial / Q000096:biosynthesis; D002648:Child; D002675:Child, Preschool; D004167:Diphtheria Toxin / Q000276:immunology; D015721:Diphtheria-Tetanus-Pertussis Vaccine / Q000008:administration & dosage* / Q000276:immunology*; D022681:Diphtheria-Tetanus-acellular Pertussis Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D006801:Humans; D007117:Immunization, Secondary; D016032:Randomized Controlled Trials as Topic; D013744:Tetanus Toxin / Q000276:immunology; D010566:Virulence Factors, Bordetella / Q000276:immunology
D000907:Antibodies, Bacterial; D004167:Diphtheria Toxin; D015721:Diphtheria-Tetanus-Pertussis Vaccine; D022681:Diphtheria-Tetanus-acellular Pertussis Vaccines; D013744:Tetanus Toxin; D010566:Virulence Factors, Bordetella