Characteristics of Serotype 3 Invasive Pneumococcal Disease before and after Universal Childhood Immunization with PCV13 in Massachusetts

Background: Although a substantial decline in vaccine-serotype invasive pneumococcal disease (IPD) incidence was observed following the introduction of pneumococcal conjugate vaccines (PCV), the estimated range of thirteen-valent conjugate vaccine (PCV13) effectiveness for serotype 3 disease is wide and includes zero. We assessed the impact of PCV13 on serotype 3 IPD incidence and disease characteristics in Massachusetts' children. Methods: Serotype 3 IPD cases in children <18 years old were identified via enhanced passive surveillance system in Massachusetts. We compared incidence rates and characteristics of IPD cases before and after PCV13. Results: A total of 47 serotype 3 IPD cases were identified from 2002 to 2017; incidence of serotype 3 IPD in the years following PCV13 was 0.19 per 100,000 children compared to 0.21 before PCV 13, incidence rate ratio (IRR) = 0.86 (95% CI 0.47-1.57). The majority (78%) of post-PCV13 serotype 3 IPD cases occurred among fully vaccinated children. Age distribution, clinical syndrome and presence of comorbidities among serotype 3 IPD cases were similar before and after PCV13 introduction. There was no association between the date of the last PCV13 dose and time to IPD to suggest waning of immunity. Conclusions: seven years following PCV 13 we found no significant changes in serotype 3 IPD incidence or disease characteristics in children in Massachusetts.