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Characterization of Emerging Serotype 19A Pneumococcal Strains in Invasive Disease and Carriage, Belgium
Insights
Following a switch to pneumococcal conjugate vaccine (PCV10), serotype 19A invasive pneumococcal disease (IPD) reemerged rapidly in Belgium. Specific new clones, ST416 and ST994, dominated both IPD and carriage, highlighting unpredictable strain emergence.
Area of Science:
- Microbiology
- Epidemiology
- Vaccinology
Background:
- The introduction of pneumococcal conjugate vaccines (PCVs) has significantly reduced invasive pneumococcal disease (IPD).
- Belgium transitioned from a 13-valent PCV to a 10-valent PCV (PCV10) in 2015-2016.
- An increase in serotype 19A IPD was observed post-vaccine switch.
Purpose of the Study:
- To investigate the genetic characteristics and epidemiology of serotype 19A IPD and carriage isolates following the PCV10 switch in Belgium.
- To identify dominant pneumococcal sequence types (STs) responsible for the resurgence of serotype 19A IPD.
- To compare emerging 19A strains with those prevalent before the PCV10 introduction.
Main Methods:
- Whole-genome sequencing was performed on 166 serotype 19A isolates from IPD and nasopharyngeal carriage.
- Isolates were collected from children and older adults between 2017-2018, after the PCV10 vaccine switch.
- Sequence types (STs) and their corresponding global pneumococcal sequence clusters (GPSCs) were identified and analyzed.
Main Results:
- Twenty-four distinct STs were identified among the serotype 19A isolates.
- ST416 (GPSC 4) and ST994 (GPSC 146) emerged as the predominant clones, accounting for 75.9% of pediatric IPD and 65.7% of all IPD and carriage isolates.
- These dominant STs were different from those (ST193 and ST276) prevalent after the introduction of PCV7, indicating a shift in circulating strains.
- Despite susceptible antimicrobial profiles, these clones successfully spread in both carriage and IPD during the PCV10 era.
Conclusions:
- The switch to PCV10 in Belgium was followed by a rapid reemergence of serotype 19A invasive pneumococcal disease.
- New dominant clones, ST416 and ST994, have emerged and are responsible for the majority of 19A IPD and carriage.
- The emergence of these novel clones underscores that predicting future IPD-causing strains based solely on historical data is unreliable.
- Effective control strategies may need to account for the dynamic nature of pneumococcal serotype and clone replacement.
Abstract:
After switching from 13-valent to 10-valent pneumococcal conjugate vaccine (PCV10) (2015-2016) for children in Belgium, we observed rapid reemergence of serotype 19A invasive pneumococcal disease (IPD). Whole-genome sequencing of 166 serotype 19A IPD isolates from children (n = 54) and older adults (n = 56) and carriage isolates from healthy children (n = 56) collected after the vaccine switch (2017-2018) showed 24 sequence types (STs). ST416 (global pneumococcal sequence cluster [GPSC] 4) and ST994 (GPSC146) accounted for 75.9% of IPD strains from children and 65.7% of IPD (children and older adults) and carriage isolates in the PCV10 period (2017-2018). These STs differed from predominant 19A IPD STs after introduction of PCV7 (2011) in Belgium (ST193 [GPSC11] and ST276 [GPSC10]), which indicates that prediction of emerging strains cannot be based solely on historical emerging strains. Despite their susceptible antimicrobial drug profiles, these clones spread in carriage and IPD during PCV10 use.
