Impact of PCV7/PCV13 introduction on invasive pneumococcal disease (IPD) in young children: Comparison between meningitis and non-meningitis IPD.

BACKGROUND: The worldwide introduction of pneumococcal conjugate vaccines (PCV) into National Immunization Programs resulted in rapid and substantial reduction of invasive pneumococcal disease (IPD) rates in children. However, the reduction of meningitis vs. non-meningitis IPD (nm-IPD) was not yet fully elucidated. We compared 7-valent and 13-valent PCV (PCV7 and PCV13) impact on pneumococcal-meningitis vs. nm-IPD in Israeli children <5years. METHODS: We conducted an ongoing nationwide, prospective, population-based, active surveillance. PCV7 and PCV13 were implemented in Israel in July 2009 and November 2010, respectively. All pneumococcal isolates (blood and/or CSF) from IPD episodes in children <5years from July 2000 through June 2015 were included. Extrapolation for missing serotypes (34.7% of all isolates) was conducted. RESULTS: 4163 IPD cases were identified; 3739nm-IPD (89.8%) and 424 meningitis (10.2%). During the pre-PCV period (2000-2008), children <12months constituted 52.1% and 33.7% of meningitis and nm-IPD, respectively (p<0.001). The respective proportions of non-PCV13 serotypes (non-VT) were 18.2% vs. 10.1%, (p<0.001). Comparing the last study year (2014-2015) to the mean of pre-PCV period, meningitis incidence in children <5years decreased non-significantly by 27%, while nm-IPD decreased significantly by 69%. Dynamic rates of meningitis and nm-IPD caused by PCV13 serotypes were similar, with 93% and 95% overall reductions, respectively. However, non-VT increased in meningitis relatively to nm-IPD, mainly in children <24months. Serotype 12F rose sharply and significantly since 2009-2010 through 2014-2015 (28.6% of all non-VT meningitis in children <24m). CONCLUSIONS: The overall impact of PCV7/PCV13 in children <5years in Israel was less prominent in meningitis than in nm-IPD. This could be attributed to the younger age of children with meningitis and differences in causative serotypes between the two groups, as the decline of the incidence of meningitis and nm-IPD caused by vaccine-serotypes is similar. Continuous monitoring of meningitis and nm-IPD is warranted.