Vaccination of Icelandic children with the 10-valent pneumococcal vaccine leads to a significant herd effect among adults in Iceland

• Published in: Journal of Clinical Microbiology
• Main Authors: Quirk, SJ, Haraldsson, G, Hjálmarsdóttir, MÁ, Van Tonder, AJ, Hrafnkelsson, B, Bentley, SD, Haraldsson, Á, Erlendsdóttir, H, Brueggemann, AB, Kristinsson, KG
• Other Authors: Wellcome Trust, GlaxoSmithKline, John Fell Fund, University of Oxford
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Society for Microbiology 2019
• Subjects: Science & Technology; Life Sciences & Biomedicine; Microbiology; Iceland; Streptococcus pneumoniae; adults; epidemiology; lower respiratory tract; molecular epidemiology; pneumococcus; pneumonia; vaccination; NONINVASIVE STREPTOCOCCUS-PNEUMONIAE; NONTYPABLE HAEMOPHILUS-INFLUENZAE; COMMUNITY-ACQUIRED PNEUMONIA; ACUTE OTITIS-MEDIA; CONJUGATE VACCINE; SEROTYPE REPLACEMENT; PEDIATRIC-PATIENTS; DISEASE; IMPACT; PCV13; 06 Biological Sciences; 07 Agricultural and Veterinary Sciences; 11 Medical and Health Sciences
• Online Access: http://hdl.handle.net/10044/1/69272; https://doi.org/10.1128/JCM.01766-18

The introduction of pneumococcal conjugate vaccines (PCV) into childhood vaccination programs has reduced carriage of vaccine serotypes and pneumococcal disease. The 10-valent PCV was introduced in Iceland in 2011. The aim of this study was to determine PCV impact on the prevalence of serotypes, genetic lineages and antimicrobial-resistant pneumococci isolated from the lower respiratory tract (LRT) of adults.Pneumococci isolated during 2009-2017 at the Landspitali University Hospital, were included (n=797). The hospital serves almost three-quarters of the Icelandic population. Isolates were serotyped and tested for antimicrobial susceptibility, and the genome of every other isolate from 2009-2014 was sequenced (n=275). Serotypes and multilocus sequence types (STs) were extracted from the genome data. Three study periods were defined: 2009-2011 (PreVac), 2012-2014 (PostVac-I) and 2015-2017 (PostVac-II).The total number of isolates and vaccine-type (VT) pneumococci decreased from PreVac to PostVac-II (n=314 vs n=230; p=0.002 and n=170 vs n=33; p<0.001, respectively), but nonvaccine-type (NVT) pneumococci increased among adults 18-64 years old (n=56 vs n=114; p=0.008). Serotype 19F decreased in the PostVac-II period: these isolates were all multidrug-resistant (MDR) and were members of the Taiwan19F-14 PMEN lineage. Serotype 6A decreased among adults ≥65 years old PostVac-II (p=0.037), while serotype 6C increased (p=0.021) and most serotype 6C isolates were MDR. Non-encapsulated S. pneumoniae (NESp) increased among adults 18-64 years old PostVac-II and the majority were MDR (p=0.028).An overall reduction in the number of LRT samples, pneumococcal-positive cultures, and significant changes in the serotype distribution became evident within four years thereby demonstrating a significant herd effect.