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BACKGROUND: Streptococcus pneumoniaeis a leading cause of severe pneumonia, bacteremia, and meningitis in young children. Two childhood vaccines have been introduced: the 7-valent pneumococcal vaccine (PCV7) in 2000 and the 13-valent pneumococcal vaccine (PCV13) in 2010. PCV13 is recommended for all children 2-59 months of age, and children at increased risk 60-71 months of age. The New York State Emerging Infections Program’s Active Bacterial Core surveillance has conducted population-based surveillance for invasive pneumococcal disease (IPD) in 15 upstate counties since 1999, and expanded to include one additional county in 2005. This analysis aims to assess incidence of IPD in children <5 years following the introduction of pneumococcal vaccines.
METHODS: IPD case isolates were sent to the state laboratory for confirmation and forwarded to CDC for serotyping. Cases’ laboratory results were linked to case reports from 1999-2013 for the 15 original counties and from 2005-2013 for the added county in SAS 9.3. Incidence rates (IR) were calculated per 100,000 population and chi-squared test for trend was used to test significance.
RESULTS: Between 1999 and 2013, 580 IPD cases in children <5 years were reported in the catchment; 550 (94.8%) were serotyped. Overall IPD incidence significantly decreased after vaccine introduction, from 81.8 cases/100,000 in 1999 to 11.6 cases/100,000 in 2013 (p<0.001). In 1999, 79.6% of isolates expressed a PCV7 serotype, compared to 0% from 2009-2013. In 2009, before introduction of PCV13, 63.9% of isolates expressed a PCV13 serotype (the 6 added serotypes), compared to 22.2% in 2013. Incidence of non-vaccine serotypes increased from 1999 to 2013 (IR=5.5 vs 8.5, p=0.035). IPD incidence decreased most dramatically following PCV7, with the steepest decline in black children (IR=188.4 in 1999 vs 16.7 in 2003, p<0.001). PCV13 introduction had a larger impact among black children as well; incidence among white children remained relatively stable from 2003-2013, whereas incidence among black children began to increase after the initial PCV7 reductions. The disparity in IPD that existed between black and white children in 1999 (IR=188.4 in blacks vs 60.5 in whites) was attenuated overtime, but it is difficult to discern any patterns in incidence post-PCV13 due to the low, fluctuating number of cases each year.
CONCLUSIONS: IPD incidence in children <5 years significantly declined following the introduction of PCV7, and continued to decline following PCV13 introduction. Strong surveillance remains necessary to monitor changes in serotype distribution post-PCV13 and to assess continued impact of vaccine on disease disparities.