Invasive pneumococcal pneumonia caused by 13-valent pneumococcal conjugate vaccine types in children with different schedules.

Background: In Taiwan, the age group with the greatest incidence of invasive pneumococcal disease is 2-5 years of age, which is different from other countries. This study was conducted to identify risk factors and different 13-valent pneumococcal conjugate vaccine (PCV13) schedules associated with vaccine-type invasive pneumococcal pneumonia (IPP) despite prior vaccination.

Methods: A case-control study was conducted prospectively between August 2012 and December 2015 at five participating medical centers. The study enrolled children <15 years of age who were admitted to one of the five medical centers for CAP. Blood samples and acute-phase serum specimens were collected and Streptococcus pneumoniae was identified by using a real-time polymerase-chain-reaction (RT-PCR) assay targeting the lytA gene.

Results: A total of 25 children diagnosed with vaccine-type IPP and 124 controls were enrolled. Vaccine-type IPP occurred in 6 (28.6%), 14 (24.1%), and 5 (7.1%) children receiving vaccines on a not-age-appropriate schedule (n = 21), primary infant schedule (n = 58), and toddler catch-up schedule (n = 70) (P = 0.008), respectively. Of 25 children, the mean age at disease onset was 36 ± 11 months; serotype 19A was responsible for 84% (21/25).

Conclusion: After adjustment for confounding factors, the risk of vaccine-type IPP was significantly higher among children receiving vaccines on a not-age-appropriate schedule, or on a primary infant schedule, compared with children receiving vaccines on a toddler catch-up schedule. Duration of vaccine immunity should be investigated to direct strategies for maintaining individual and population immunity against pneumococcal disease.