PCV13 serotype decrease in Italian adolescents and adults in the post-PCV13 era: Herd protection from children or...

Area of Science:

• Infectious Diseases
• Epidemiology
• Vaccinology

Background:

• The pediatric vaccination schedule in Italy transitioned from pneumococcal conjugate vaccine 7 (PCV7) to PCV13 in 2010.
• While PCV7 demonstrated a clear herd effect, the herd effect of PCV13 remains under investigation.
• Understanding serotype distribution shifts in unvaccinated populations is crucial for evaluating vaccine impact.

Purpose of the Study:

• To assess changes in pneumococcal serotype distribution in unvaccinated Italian adolescents and adults.
• To compare serotype prevalence between the pre- and post-PCV13 vaccination eras.
• To evaluate the potential herd effect of PCV13 in a high-childhood-vaccination region.

Main Methods:

• Retrospective study of unvaccinated adolescents and adults with laboratory-confirmed pneumococcal infections.
• Inclusion of patients from three Italian regions (Friuli-Venezia Giulia, Emilia Romagna, Tuscany) between April 2006 and June 2016.
• Diagnosis and serotyping of Streptococcus pneumoniae using Real Time PCR on sterile fluids or culture isolates.

Main Results:

• A total of 523 unvaccinated patients were analyzed; 96.4% of isolates were serotyped.
• The most common serotypes were 3, 8, and 19A.
• PCV13 serotypes decreased from 62.3% in the pre-PCV13 era to 45.0% in the post-PCV13 era (p=0.005). Serotype 7F significantly decreased from 15.6% to 2.8% (p<0.001), primarily driving this difference.

Conclusions:

• A significant shift in pneumococcal serotype distribution was observed in unvaccinated adolescents and adults following PCV13 introduction.
• The reduction in serotype 7F prevalence suggests a potential indirect (herd) effect of pediatric PCV13 vaccination.
• Targeted vaccination programs for adults, particularly the elderly, are recommended to further reduce pneumococcal disease burden.