title: PCV13 serotype decrease in Italian adolescents and adults in the post-PCV13 era: Herd protection from children or secular trend?
abstract: In 2010 PCV13 replaced PCV7 in the pediatric vaccination schedule for Italian children. While a strong herd effect was demonstrated for PCV7, a possible herd effect due to PCV13 is still under debate. Our aim was to evaluate differences in the distribution of pneumococcal serotypes between the pre and post-PCV13 eras in unvaccinated Italian adolescents and adults with laboratory-confirmed pneumococcal infection from 3 Italian Regions with a high rate of PCV13 vaccination of children.
  
  
  
  Adolescents and adults admitted with laboratory-confirmed pneumococcal infection in the hospitals of 3 Italian Regions (Friuli-Venezia Giulia, Emilia Romagna, and Tuscany) between April 2006 and June 2016 were included in the study. Diagnosis of pneumococcal infection and serotyping were performed with Real Time PCR directly on normally sterile fluids or on culture isolates.
  
  
  
  523 patients with laboratory-confirmed pneumococcal infection were enrolled (Male/Female ratio was 300/223, 1.3; median age 67.1, IQR 53.4-74.9). None of the patients had been vaccinated with any pneumococcal vaccine; 96.4% were serotyped. Overall, the most frequent serotypes were 3 (67/504, 13.3%), 8 (43/504, 8.5%), and 19A (38/504, 7.5%). Serotype distribution differed among age classes and clinical presentations. Overall, PCV13 serotypes accounted for 47.6% of cases: 62.3% in the pre-PCV13 era and 45.0% in the post-PCV13 era; (p=0.005 OR=2.03; CL 95%: 1.2-3.3). Serotype 7F accounted for 12/77 (15.6%) of all serotypes in the pre-PCV13 period and for 12/427 (2.8%) in the post-PCV13 period and was the only serotype significantly contributing to the difference in percentage between pre and post-PCV13 eras.
  
  
  
  Our study demonstrated a difference in percentage in serotype distribution in adolescents and adults laboratory-confirmed pneumococcal infection between the pre and post-PCV13 eras. This difference is mainly due to the decrease of serotype 7F. Thus, in order to decrease disease burden, adults and in particular the elderly should be offered a specific vaccination program.
authors.affiliation: Division of Immunology, Section of Pediatrics, Department of Health Sciences, University of Florence and Anna Meyer Children's Hospital, Florence, Italy. Electronic address: francesco.nieddu@meyer.it.
authors.forename: Francesco
authors.initials: F
authors.lastname: Nieddu
authors.affiliation: Division of Immunology, Section of Pediatrics, Department of Health Sciences, University of Florence and Anna Meyer Children's Hospital, Florence, Italy.
authors.forename: Maria
authors.initials: M
authors.lastname: Moriondo
authors.affiliation: Division of Immunology, Section of Pediatrics, Department of Health Sciences, University of Florence and Anna Meyer Children's Hospital, Florence, Italy.
authors.forename: Elisa
authors.initials: E
authors.lastname: De Vitis
authors.affiliation: Division of Immunology, Section of Pediatrics, Department of Health Sciences, University of Florence and Anna Meyer Children's Hospital, Florence, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Ricci
authors.affiliation: Division of Immunology, Section of Pediatrics, Department of Health Sciences, University of Florence and Anna Meyer Children's Hospital, Florence, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Indolfi
authors.affiliation: Pediatric Division, Anna Meyer Children's Hospital, Florence, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Resti
authors.affiliation: Unit of Microbiology, Regional Reference Centre for Microbiological Emergencies (CRREM), St Orsola Malpighi Hospital, Bologna, Italy.
authors.forename: Caterina
authors.initials: C
authors.lastname: Vocale
authors.affiliation: Unit of Microbiology, Regional Reference Centre for Microbiological Emergencies (CRREM), St Orsola Malpighi Hospital, Bologna, Italy.
authors.forename: Maria Paola
authors.initials: MP
authors.lastname: Landini
authors.affiliation: AOU S. Maria della Misericordia, Microbiology Laboratory, Udine, Italy.
authors.forename: Assunta
authors.initials: A
authors.lastname: Sartor
authors.affiliation: Division of Immunology, Section of Pediatrics, Department of Health Sciences, University of Florence and Anna Meyer Children's Hospital, Florence, Italy.
authors.forename: Chiara
authors.initials: C
authors.lastname: Azzari
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D032521:Immunity, Herd; D007558:Italy / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D011008:Pneumococcal Infections / Q000453:epidemiology* / Q000382:microbiology*; D022242:Pneumococcal Vaccines / Q000276:immunology*; D015995:Prevalence; D065288:Serogroup; D013296:Streptococcus pneumoniae / Q000145:classification* / Q000302:isolation & purification; D055815:Young Adult
chemical_list: C538862:13-valent pneumococcal vaccine; D022242:Pneumococcal Vaccines
keywords: 13-Valent pneumococcal conjugate vaccine; Adults; Herd protection; Invasive pneumococcal disease; Serotypes; Streptococcus pneumoniae