Progressive changes in pneumococcal carriage in children attending daycare in Portugal after 6 years of gradual conjugate vaccine introduction show falls in most residual vaccine serotypes but no net replacement or trends in diversity.

OBJECTIVES: To track ongoing trends in pneumococcal (Sp) serotype carriage under the selection pressure of moderate pneumococcal conjugate vaccine (PCV) use, children in a community in Portugal were studied in the same months in 3 consecutive years.
METHODS: Nasopharyngeal specimens were collected (children aged 3 months to <7 years) in 8 urban daycare centers in February 2008 (n=561) and 2009 (n=585). Sp isolates were serotyped.
RESULTS: While demographics were similar in 2008-2009 and a previously reported sample in 2007, PCV coverage (at least one dose) in the children studied rose from 76.5% to 84% although national coverage was lower than this. Sp carriage fell from 61% to 51% with a concomitant fall in PCV7 serotype carriage from 12.1% to 4.3%. Remaining PCV7 serotypes declined to near (23F) or totally (6B, 14) undetectable levels except 19F which persisted unchanged in around 4% of children. Although carriage of 3 and 6C rose, there was no net increase in non-PCV7 serotypes and no progressive trend in serotype diversity.
CONCLUSIONS: Ecological changes induced by PCVs where uptake is moderate appear to be different from high usage settings. We report falling Sp carriage due to PCV7 serotype disappearance with persistence of 19F and no ongoing net replacement after several years of PCV7 use and slowly rising uptake.