Effect of vaccination on pneumococci isolated from the nasopharynx of healthy children and the middle ear of children with otitis media in Iceland

Vaccination with pneumococcal conjugate vaccines (PCVs) disrupts the pneumococcal population. Our aim was to determine the impact of the 10-valent PCV on the serotypes, genetic lineages and antimicrobial susceptibility of pneumococci isolated from children in Iceland. Pneumococci were collected between 2009-2017 from the nasopharynx of healthy children attending 15 day-care centres and from the middle ear (ME) of children with acute otitis media from the greater Reykjavik capital area. Isolates were serotyped and tested for antimicrobial susceptibility. Whole genome sequencing (WGS) was performed on alternate isolates from 2009-2014 and serotypes and multilocus sequence types (STs) were extracted from the WGS data. Two study periods were defined: 2009-2011 (PreVac) and 2012-2017 (PostVac). The overall nasopharyngeal carriage rate was similar between the two periods (67.3% PreVac and 61.5% PostVac, p=0.090). Vaccine-type (VT) pneumococci decreased and nonvaccine-type (NVT) pneumococci (serotypes 6C, 15A, 15B/C, 21, 22F, 23A, 23B, 35F, 35B) significantly increased post-PCV introduction in different age strata. The total number of pneumococci recovered from ME samples significantly decreased, as did the proportion that were VTs, although NVT pneumococci (6C, 15B/C, 23A and 23B) increased significantly. Most serotype 6C pneumococci were multidrug-resistant (MDR). Serotype 19F was the predominant serotype associated with ME and it significantly decreased post-PCV introduction: these isolates were predominantly MDR and of the Taiwan19F-14 PMEN lineage. Overall, the nasopharyngeal carriage rate remained constant and the number of ME-associated pneumococci decreased significantly post-PCV introduction; however, there was a concomitant and statistically significant shift from VTs to NVTs in both collections of pneumococci

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

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