Impact of Introduction of Conjugate Vaccines in the Vaccination Schedule on the Incidence of Pediatric Invasive Pneumococcal Disease Requiring Hospitalization in Madrid 2007 to 2011

Background: Differences in invasive pneumococcal disease (IPD) in children are expected after a change from 7-valent pneumococcal conjugate vaccine (PCV7) to 13-valent pneumococcal conjugate vaccine (PCV13). Universal vaccination with PCV7 started in Madrid in November 2006, and it switched to PCV13 in June 2010. Methods: A prospective, laboratory-confirmed (by culture or polymerase chain reaction), clinical surveillance including all pediatric IPD requiring hospitalization in Madrid was performed in all hospitals with a pediatric department and included four 1-year periods from May 2007 to April 2011. Incidence rate (IR) was calculated as number cases per 100,000 inhabitants using children population data. Results: Six hundred fourteen IPDs were identified: 209 parapneumonic pneumococcal empyema, 191 bacteremic pneumonia, 75 primary bacteremia, 72 meningitis, 38 IPDs secondary to otic foci and 29 others. The incidence of IPD remained unchanged during 2007-2010 (IR=approximate to 17.0), with a marked decrease in 2010-2011 (IR= 11.34; P<0.05) attributable to reduction in children younger than 24 months (50.19 in 2008-2009 compared with 24.92 in 2010-2011; P<0.005). The incidence of bacteremic pneumonia (R-2=0.966; beta=1.132; P=0.017) and meningitis (R-2=0.898; beta=0.505; P=0.052) showed decreasing linear trends over time. The incidence of parapneumonic pneumococcal empyema increased in 2009-2010 but decreased in 2010-2011 (6.73 vs. 4.14; P=0.019). The incidence of IPDs by PCV13 serotypes was significantly (P <= 0.004) lower in 2010-2011 (8.78) than in previous periods (IR=approximate to 13.5). Conclusions: Early data regarding changing from PCV7 to PCV13 use in the childhood vaccination calendar indicate that reductions in IR of bacteremic pneumonia and meningitis after PCV7 introduction (by reduction of cases by serotypes 1 and 19A) further decreased and there was a reversion of the increase in IR of parapneumonic pneumococcal empyema from 2010-2011, mainly because of reduction in serotype 1 and 19A cases.