The herd effects of infant PCV7/PCV13 sequential implementation on adult invasive pneumococcal disease, six years post implementation; a nationwide study in Israel

Background Introduction of pneumococcal conjugate vaccine (PCV) has nearly eliminated vaccine-type (VT) invasive pneumococcal disease (IPD) in children, yet the reported resulting reduction of adult IPD is variable. We present the indirect impact of sequential PCV7/PCV13 implementation in Israel on adult IPD. Methods An ongoing nationwide active surveillance was initiated on July 2009 when PCV7 was implemented (with Catch-up). PCV7 was gradually replaced by PCV13 since November 2010. Comorbidity and outcome data were collected from medical files. Incidence rates were calculated for overall and vaccine-type IPD. Results A total of 2579 IPD cases were diagnosed among a population of 5.0–5.5 million adults >18y (2009–2015). Incidence rates were 9.15/100,000 and 10.16/100,000 in the first and second study years, respectively. However, after PCV13 implementation, the rates decreased to 7.19 within four years, and remained stable in the two following years. Within 6 years, PCV7-VT-IPD incidence decreased from 2.52 to 0.52 (79%) and PCV13-VT-IPD from 6.15 to 1.81 (71%). Concurrently, non-VT13 incidence increased from 2.99 to 5.25. Approximately 50% of all patients were adults ≥65y, in whom the decrease in PCV13-VT-IPD incidence was smaller and slower (65% vs. >80% decrease in adults <50y). Conclusions Despite continued reduction in PCV13-VT-IPD, overall IPD was stable during the last two years due to serotype replacement. Yet, the significant decrease in adult IPD, six years post-PCV7/13 implementation emphasizes the importance of indirect protection in achieving overall population impact and should be considered when discussing the potential additional benefits of direct adult PCV vaccination.