Authors: Nicola Principi, Leonardo Terranova, Alberto Zampiero, Valentina Montinaro, Valentina Ierardi, Walter Peves Rios, Claudio Pelucchi, Susanna Esposito

Title: Pharyngeal colonisation by streptococcus pneumoniae in older children and adolescents in a geographical area characterised by relatively limited pneumococcal vaccination coverage

Summary

The aim of this study, published on the last issue of The Pediatric Infectious Disease Journal, was to evaluate the relationships between colonisation and vaccination status with pneumococcal conjugate vaccine (PCV) in older children and adolescents living in an area characterised by relatively limited vaccination coverage.

Oropharyngeal swabs were obtained from 2,076 randomly selected healthy school-age children and adolescents, and the extracted genomic DNA was tested for Streptococcus pneumoniae by means of real-time polymerase chain reaction. All of the positive cases were subsequently serotyped, and the association between vaccination status with the heptavalent PCV (PCV7) and pneumococcal colonisation was determined.

S. pneumoniae was identified in the oropharyngeal swabs of 1,201 subjects (57.9%), and its prevalence declined with age (74.9% in subjects aged
This study has several peculiarities. First of all, it was carried out with the most effective means of evaluating pneumococcal colonisation. Secondly, it involved older children and adolescents, who are rarely included in studies of the impact of infant PCV administration on the pharyngeal colonisation by pneumococci. Third, it was carried out in a geographical area in which pneumococcal vaccination coverage had been no higher than 50% for about 4 years before the beginning of the study Finally, the inclusion of both vaccinated and unvaccinated subjects made it possible to analyse the long-term effects of PCV7 on both in a setting characterised by a high rate of transmission.

These results show the absence of any long-term effect of PCV7 on colonisation, and raise doubts concerning the recent suggestion to use carriage to evaluate the efficacy of PCVs. The high prevalence of carriers in all of the age groups independently from previous pneumococcal vaccination seems to indicate that further studies are needed to evaluate whether the extensive use of PCVs in healthy older children and adolescents might be useful to persistently reduce pharyngeal colonisation of these subjects thereby increasing herd immunity.

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