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Clinical and Vaccine Immunology, May 2007, p. 593-599, Vol. 14, No. 5
1071-412X/07/$08.00+0 doi:10.1128/CVI.00344-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Oxford Vaccine Group, Centre for Clinical Vaccinology and Tropical Medicine, University of Oxford, Oxford, United Kingdom,1 Department of Immunology, Churchill Hospital, Oxford, United Kingdom,2 Centre for Statistics in Medicine, Wolfson College Annexe, University of Oxford, Oxford, United Kingdom,3 Academic Department of Microbiology and Infectious Disease, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom4
Received 7 September 2006/ Returned for modification 31 October 2006/ Accepted 21 February 2007
Children who have siblings and/or who attend day care have higher rates of nasopharyngeal colonization with pneumococci than lone children do. Pneumococcal colonization is usually asymptomatic but is a prerequisite for invasive disease. We studied the effect of social mixing with other children on immunity to a pneumococcal vaccine. One hundred sixty children aged 1 year were immunized with a 7-valent conjugate pneumococcal vaccine. A blood sample was obtained before and 9 to 11 days after the vaccine. The concentration and avidity of antibody against vaccine pneumococcal serotypes (4, 6B, 9V, 14, 18C, 19F, and 23F) were studied in relation to pneumococcal carriage rate and measures of social mixing. Children with increased social mixing had higher antibody concentrations against serotypes 4, 9V, 14, and 23F than lone children did. The least-carried serotype, serotype 4, was the one of the most immunogenic. This contrasts with serotype 6B, the most common nasopharyngeal isolate but the least immunogenic. Social mixing in infancy enhances the immune response to a Streptococcus pneumoniae polysaccharide-protein conjugate vaccine at 1 year of age. Exposure to pneumococci in the first year of life may induce immunological priming. An alternative explanation is that differences in immunological experience, such as increased exposure to respiratory viral infections in early childhood, alters the response to vaccines perhaps by affecting the balance between Th1 and Th2 cytokines. The low immunogenicity of serotype 6B polysaccharide might make conditions more favorable for carriage of the 6B organism and explain why 6B pneumococci were more frequently isolated than other serotypes.
Published ahead of print on 7 March 2007.
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