Send to

Choose Destination
J Clin Microbiol. 2019 Mar 28;57(4). pii: e01766-18. doi: 10.1128/JCM.01766-18. Print 2019 Apr.

Vaccination of Icelandic Children with the 10-Valent Pneumococcal Vaccine Leads to a Significant Herd Effect among Adults in Iceland.

Author information

University of Iceland, Faculty of Medicine, Reykjavík, Iceland.
Landspitali, University Hospital, Reykjavík, Iceland.
BioMedical Centre of the University of Iceland, Reykjavík, Iceland.
Parasites and Microbes, Wellcome Sanger Institute, Hinxton, United Kingdom.
University of Iceland, Department of Mathematics, Reykjavík, Iceland.
Children's Hospital Iceland, Reykjavík, Iceland.
Nuffield Department of Medicine, University of Oxford, Oxford, United Kingdom.
Department of Medicine, Imperial College London, London, United Kingdom.
University of Iceland, Faculty of Medicine, Reykjavík, Iceland


The introduction of pneumococcal conjugate vaccines (PCVs) 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 between 2009 and 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 collected between 2009 and 2014 was sequenced (n = 275). Serotypes and multilocus sequence types (STs) were extracted from the genome data. Three study periods were defined, 2009 to 2011 (PreVac), 2012 to 2014 (PostVac-I), and 2015 to 2017 (PostVac-II). The total number of isolates and vaccine-type (VT) pneumococci decreased from PreVac to PostVac-II (n = 314 versus n = 230 [p = 0.002] and n = 170 versus n = 33 [p < 0.001], respectively), but non-vaccine-type (NVT) pneumococci increased among adults 18 to 64 years old (n = 56 versus 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 in the PostVac-II period (p = 0.037), while serotype 6C increased (p = 0.021) and most serotype 6C isolates were MDR. Nonencapsulated Streptococcus pneumoniae (NESp) isolates increased among adults 18 to 64 years old in the PostVac-II period, and the majority were MDR (p = 0.028). An overall reduction in the number of LRT samples and pneumococcus-positive cultures and significant changes in the serotype distribution became evident within 4 years, thereby demonstrating a significant herd effect.


Iceland; Streptococcus pneumoniae ; adults; epidemiology; lower respiratory tract; molecular epidemiology; pneumococcus; pneumonia; vaccination

[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for HighWire Icon for PubMed Central
Loading ...
Support Center