Towards the 13-valent pneumococcal conjugate universal vaccination: effectiveness in the transition era between PCV7 and PCV13 in Italy, 2010-2013.

Pneumococcal disease epidemiology has changed after introduction of pneumococcal conjugate vaccines. Seven-valent vaccine (PCV7) has been effective in reducing invasive pneumococcal disease (IPD). In Europe, PCV13 effectiveness was estimated at 78% (95% CI: -18-96%) for 2-priming doses. In Italy, PCV7 was introduced in 2006 in the childhood immunization schedule and replaced with PCV13 in 2010. In Apulia, vaccination coverage has reached 95.1% (birth-cohort 2010). We estimated PCV program effectiveness and its impact on S. pneumoniae diseases. PCV EFFECTIVENESS: We used the screening method. We calculated the Proportion of Population Vaccinated from immunization registries and detected cases through a laboratory-confirmed surveillance among hospitalized children≤60 months. A confirmed IPD case was a child with PCR positive for S. pneumoniae. Differences among children were assessed with the Chi-square or the Fisher exact test (P value<0.05). PCV IMPACT: We constructed time series using outcome-specific Poisson regression models: hospitalization rate in pre-PCV era and hospitalization risk ratios (RRs) with 95% CIs for both PCV7 and PCV7/PCV13 shifting era. We calculated hospitalization RR with 95% CIs comparing pre-PCV years with vaccination period. The PCV effectiveness was 84.3% (95% CI: 84.0-84.6%). In May 2010-January 2013, we enrolled 159 suspected IPD of whom 4 were confirmed. Two (fully vaccinated) were caused by serotype 9V, 1 (not vaccinated) by serotype 3, 1 (vaccinated with 2 PCV13 doses) by 15B/C. The most important reduction was for pneumococcal pneumonia (RR: 0.43, 95% CI: 0.21-0.90). The PCV program show promising results in terms of both PCV13 effectiveness and its impact in reducing IPD in children<5 years.