Objectives: Our aim was to compare serotype distribution in invasive pneumococcal disease (IPD) in the Belgian population before and after introduction of the 13-valent conjugte vaccine (PCV13) in the national childhood vaccination schedule.Methods: Serotyping was performed on 12,534 pleural fluid and bacteraemic Streptococcus pneumoniae isolates sent to the National Reference Centre. We compared the distribution of serotypes (ST)/serogroups (SG) between the periods before (2007-2010) and after (2012-2015) the introduction of PCV13, in children and adults of different age groups, including older individuals (65-84 and ≥85 years).Results: The introduction of PCV13 in the childhood immunization program resulted in a reduction of 16% of all IPD-isolates. The prevalence of PCV13-SG decreased in all age groups: from 81% to 53% (p < 0.0001) in children <18 years, and from 69% to 53% (p < 0.0001) in individuals aged 18-64. This effect was also observed in age groups 65-84 (64% to 50%, p < 0.0001) and ≥85 years (63% to 47%; p < 0.0001). The proportion of IPD cases caused by non-PCV13 SG increased from 31% to 49% between the two periods, indicating replacement with non-vaccine SG. The coverage rate for the 23-valent polysaccharide vaccine (PPV23) in all age groups remains as high as 89% for the total group.Conclusion: After introduction of PCV13, a reduction of PCV13-serotypes occurred in IPD in all age groups. This supports the rationale to combine the effect of PCV13 with the broader coverage of PPV23 as a vaccination strategy for adults.
Keywords: Invasive pneumococcal disease; herd protection; pneumococcal vaccination; serotype replacement; vaccine coverage.