The Impact of Pneumococcal Conjugate Vaccine (PCV) Coverage Heterogeneities on the Changing Epidemiology of Invasive Pneumococcal Disease in Switzerland, 2005-2019

Abstract

Pneumococcal conjugate vaccines (PCVs) have lowered the incidence of invasive pneumococcal disease (IPD) worldwide. However, the influence of regional vaccine uptake differences on the changing epidemiology of IPD remains unclear. We aimed to examine the overall impact of both seven- and 13-valent PCVs (PCV7 and PCV13) on IPD in Switzerland. Three-year periods from 2005-2010 and 2011-2019 were considered, respectively, as (early and late) PCV7 eras and (early, mid and late) PCV13 eras. Vaccine coverage was estimated from a nationwide survey according to east (German-speaking) and west (French/Italian-speaking) regions for each period. Reported incidence rate ratios (IRRs) were compared between successive periods and regions using nationwide IPD surveillance data. Overall IPD incidence across all ages was only 16% lower in the late PCV13 era compared to the early PCV7 era (IRR 0.83, 95% CI 0.79-0.88), due to increasing incidence of non-PCV-type IPD (2.59, 2.37-2.83) in all age groups, except children <5 years. PCV uptake rates in swiss children were slightly higher in the west than the east (p < 0.001), and were accompanied by lower IPD incidences across all age groups in the former region. Post-PCV13, non-PCV serotypes 8, 22F and 9N were the major cause of IPD in adults ≥65 years. Increased PCV coverage in both areas of Switzerland resulted in a decrease in vaccine-type and overall IPD incidence across all age groups, in a regionally dependent manner. However, the rising incidence of non-vaccine-type IPD, exclusive to older adults, may undermine indirect beneficial effects.

Keywords: Streptococcus pneumoniae; Switzerland; capsular polysaccharide; pneumococcal conjugate vaccines (PCVs); serotype 3.

Figure 1

Incidence of invasive pneumococcal disease in Switzerland during 2005–2019. Overall incidence stratified by (A) age group, (B) vaccine serotype and (C) age group and vaccine serotype. Introduction of PCV7 (2006) and PCV13 (2011) are indicated by dotted black lines.

Figure 2

Single Serotype analyses in Switzerland, 2005–2019. Single serotypes with high IPD incidences are indicated. Certain serotypes have not been part of the routine typing in Switzerland for 2005–2006 (hence the data is shaded). Introduction of PCV7 (2006) and PCV13 (2011) are indicated by dotted black lines.

Figure 3

Incidence of invasive pneumococcal disease by region in Switzerland, 2005–2019. Regional incidence is illustrated (A) overall and (B) stratified by vaccine serotype. 95% confidence intervals are depicted as the shaded region between ribbon dashed lines. Introduction of PCV7 (2006) and PCV13 (2011) are indicated by dotted black lines.

Figure 4

Timeliness of pneumococcal conjugate vaccine uptake, regional estimates of coverage and age-group specific incidence in Switzerland, 2005–2019.(A) Timeliness of vaccine uptake in children aged 2-years, vaccinated with 1–3 doses of PCV7 or PCV13, (B) age group-specific IPD incidence and regional estimates of pneumococcal vaccination coverage among children aged 2-years with 1–2 PCV doses, and (C) age group- and region-stratified IPD incidence by vaccine serotypes. 95% confidence intervals are depicted by (A) shaded regions and (B) error bars. For the combined graph (B), the primary Y-axis shows the IPD cases per 100′000 population (line graph) and the secondary Y-axis shows the vaccine uptake rates (bar graph). Introduction of PCV7 (2006) and PCV13 (2011) are indicated by dotted black lines (C). Proportions and vaccination coverage estimate during the 2005–2007 period were excluded due to very low rates (<3%). *** indicates p < 0.001 (Two proportions z-test).