METHODS: Pneumococcal sterile site isolates, reported through state-wide surveillance, were serotyped using standard methods. We defined a pre-PCV13 time period 2005-2008 and post-PCV13 time period 2011-2015; excluding 2009–2010 because PCV13 was introduced pre-licensure in one high-risk region in 2009.
RESULTS: Among Alaska children <5 years, PCV13 serotypes comprised 62% of IPD in the pre-PCV13 period and 22% in the PCV13 period. Among all Alaska children <5 years, IPD rates decreased from 60.9 (pre) to 21.8 (post) per 100,000/yr (P<.001); PCV13 serotype IPD decreased from 37.7 to 4.8 (P<.001). Among AN children <5 years, IPD rates decreased from 149.2 to 49.8 (P<.001); PCV13 serotype IPD decreased from 87.0 to 11.8 (P<.001); non-PCV13 serotype IPD did not change significantly. Among persons > 50 years, the post-vaccine IPD rate was not significantly different from the baseline period, but declined in persons 18-49 years (45%, P<0.001); this decline was similar in AN and non-AN persons (46%, P<0.001, 46%, P<0.001, respectively).
CONCLUSIONS: Almost 6 years after PCV13 introduction, overall IPD and PCV13-serotype IPD rates have decreased substantially in Alaska children <5 years of age when compared with 2005-2008. We observed evidence of indirect effect among adults with a 45% reduction in IPD among persons 18-49 years.