Background
Ten-valent and 13-valent pneumococcal conjugate vaccines (PCVs) have shown important
benefits by decreasing invasive pneumococcal disease caused by vaccine serotypes.
Belgium had an uncommon situation with sequential use of PCV7, PCV13, and PCV10 in
the childhood vaccination programmes between 2007 and 2018. We aimed to analyse the
changes in incidence of invasive pneumococcal disease and serotype distribution in
children throughout this period.
Methods
Streptococcus pneumoniae isolates were obtained from patients with invasive pneumococcal disease in Belgium
between 2007 and 2018 by the national laboratory-based surveillance. Paediatric invasive
pneumococcal disease incidence, serotype distribution, and antimicrobial susceptibility
were analysed in periods during which PCV7 (2009–10), PCV13 (2013–14), both PCV13
and PCV10 (2015–16), and PCV10 (2017–18) were used. Incidence rates and trends were
compared. Vaccination status was collected. For a subset of serotype 19A isolates,
multilocus sequence type was identified.
Findings
After a decrease in PCV7 serotype invasive pneumococcal disease was observed during
the PCV7 period, total paediatric invasive pneumococcal disease incidence significantly
declined during the PCV13 period (−2·6% monthly, p<0·0001). During the PCV13–PCV10
period (2015–16), the lowest mean in paediatric invasive pneumococcal disease incidence
was achieved, but the incidence increased again during the PCV10 period (2017–18),
especially in children younger than 2 years (+1·7% monthly; p=0·028). This increase
was mainly due to a significant rise in serotype 19A invasive pneumococcal disease
incidence in the PCV10 period compared with the PCV13 period (p<0·0001), making serotype
19A the predominant serotype in paediatric invasive pneumococcal disease in the PCV10
period. Genetic diversity within the 2017–18 serotype 19A collection was seen, with
two predominant clones, ST416 and ST994, that were infrequently observed before PCV10
introduction. In 2018, among children younger than 5 years with invasive pneumococcal
disease who were correctly vaccinated, 37% (37 of 100) had PCV13 serotype invasive
pneumococcal disease, all caused by serotype 19A and serotype 3.
Interpretation
After a significant decrease during the PCV13 period, paediatric invasive pneumococcal
disease incidence increased again during the PCV10 period. This observation mainly
resulted from a significant increase of serotype 19A cases. During the PCV10 period,
dominant serotype 19A clones differed from those detected during previous vaccine
periods. Whether changes in epidemiology resulted from the vaccine switch or also
from natural evolution remains to be further elucidated.
Funding
The Belgian National Reference is funded by the Belgian National Institute for Health
and Disability Insurance and the whole genome sequencing by an investigator-initiated
research grant from Pfizer.
