PCV7-induced changes in pneumococcal carriage and invasive disease burden in Alaskan children.

Abstract Background Changes in pneumococcal serotype-specific carriage and invasive pneumococcal disease (IPD) after the introduction of pneumococcal conjugate vaccine (PCV7) could inform serotype epidemiology patterns following the introduction of newer conjugate vaccines. Methods We used data from statewide IPD surveillance and annual pneumococcal carriage studies in four regions of Alaska to calculate serotype-specific invasiveness ratios (IR; odds ratio of a carried serotype's likelihood to cause invasive disease compared to other serotypes) in children Results Incidence of IPD decreased from the pre- to post-vaccine period (95.7 vs. 57.2 cases per 100,000 children, P P  = 0.002) and to the Alaska post-vaccine period (Spearman's rho = 0.28, P  = 0.029). Relatively invasive serotypes (IR > 1) caused 66% of IPD in both periods, although fewer serotypes with IR > 1 remained in the post-vaccine ( n  = 9) than the pre-vaccine period ( n  = 13). Conclusions After PCV7 introduction, serotype IRs changed little, and four of the most invasive serotypes were nearly eliminated. If PCV13 use leads to a reduction of carriage and IPD for the 13 vaccine serotypes, the overall IPD rate should further decline. Note The findings and conclusions in this report are those of the author(s) and do not necessarily represent the official position of the Centers for Disease Control and Prevention.