Decreasing incidence and changes in serotype distribution of invasive pneumococcal disease in persons aged under 18 years since introduction of 10-valent and 13-valent conjugate vaccines in Portugal, July 2008 to June 2012

The 10-valent pneumococcal conjugate vaccine(PCV10) became available in Portugal in mid-2009 and the 13-valent vaccine (PCV13) in early 2010. The incidence of invasive pneumococcal disease (IPD) in patients aged under 18 years decreased from 8.19 cases per 100,000 in 2008-09 to 4.52/100,000 in 2011-12. However, IPD incidence due to the serotypesincluded in the 7-valent conjugate vaccine(PCV7) in children aged under two years remained constant. This fall resulted from significant decreases in the number of cases due to: (i) the additional serotypesincluded in PCV10 and PCV13 (1, 5, 7F; from 37.6% to 20.6%), particularly serotype1 in older children; and (ii) the additional serotypesincluded in PCV13 (3, 6A, 19A; from 31.6% to 16.2%), particularly serotype19A in younger children. The decrease in serotype19A before vaccination indicates that it was not triggered by PCV13 administration. The decrease of serotype1 in all groups, concomitant with the introduction of PCV10, is also unlikely to have been triggered by vaccination, although PCVs may have intensified and supported these trends. PCV13 serotypesremain major causes of IPD, accounting for 63.2% of isolates recovered in Portugal in 2011-12, highlighting the potential role of enhanced vaccination in reducing paediatric IPD in Portugal. .