Anneke Steens

The aim of this study was to evaluate the impact of the vaccination programme with 23-valent pneumococcal polysaccharide vaccine (PPV23) on non-invasive pneumococcal pneumonia (NIPP) in adults above 60 years old during the first three post-implementation years. For this retrospective impact study with a regression discontinuity design, we included patients aged 56 to 85 years who presented with NIPP at the hospital between November 1, 2016 and September 30, 2023. NIPP was defined as a positive pneumococcal urinary antigen test without meeting criteria for invasive pneumococcal disease (blood and/or cerebrospinal fluid culture positive for Streptococcus pneumoniae ). We estimated the overall impact and the impact stratified by time since eligibility for vaccination for each birth cohort. Data were obtained from 14 laboratories throughout the Netherlands, which were estimated to cover 34.9% of the Dutch population. We observed 3821 NIPP patients, of whom 634 were eligible for vaccination. The overall impact was 19.7% (95% confidence interval 8.5, 29.7). Impact estimates decreased over time since eligibility, although non-significantly with overlapping confidence intervals. These insights contribute to the existing body of evidence about PPV23 impact on NIPP, informing future vaccination policy.

BACKGROUND: Invasive Haemophilus influenzae type b (iHib) disease incidence in < 5-year-olds decreased after vaccine introduction but increased between 2011 and 2023 in the Netherlands. The National Immunisation Programme changed products in 2011 (from DTaP-IPV/Hib to DT3aP-HBV-IPV/Hib) and 2018 (to DT5aP-HBV-IPV-Hib) and schedule from 3 + 1 to 2 + 1 doses in 2020. AIM: We aimed to estimate overall, product- and schedule-specific vaccine effectiveness (VE) against iHib disease to inform vaccination strategies. METHODS: We conducted a matched case–control study extracting iHib cases born ≥ 2005 and aged 6–119 months from 2005–2023 national reference laboratory data. We selected 10 controls per case matched on birth date and sex from the population register and obtained vaccination data from the vaccination registry. Using conditional logistic regression, we estimated matched odds ratios (mOR) and VE among 6–10-month-olds (eligible only for the primary series) and 11–119-month-olds. RESULTS: We included 250 iHib cases and 2,487 controls. Among children aged 11–119 months, VE against iHib of the full schedule was 96% (95% CI: 88–99), 95% (95% CI: 91–97) and 98% (95% CI: 94–99) for any DTaP-IPV/Hib, DT3aP-HBV-IPV/Hib and DT5aP-HBV-IPV-Hib, respectively. It was 97% (95% CI: 93–99) for 2 + 1, 96% (95% CI: 93–98) for 3 + 1 doses, and > 95% for the respective primary series. No differences in VE by time since vaccination were observed between products or schedules. CONCLUSION: Changes in VE against iHib after recent product or schedule changes do not explain the increasing iHib incidence. The high VE supports pursuing optimal vaccination coverage.

This study assessed whether systematically using finetype data in national surveillance of invasive meningococcal disease serogroup B (IMD-B) in the Netherlands could improve cluster detection in order to prevent further cases through public health actions. We analysed 2005–2023 data, including 1,642 IMD-B cases with complete finetype and municipality information (95%; N = 1729). Using a generalized linear model, we calculated expected baselines for each finetype, including temporal trends. Using SaTScan™, we applied Poisson scan-statistics with a 365-day window to identify spatiotemporal clusters, comparing results to epidemiological and core-genome multi-locus sequence typing (cgMLST) data. Of 453 finetypes, 308 (68%) occurred once; diversity was high (Gini-Simpson index 0.96). We identified 42 spatiotemporal clusters across 37 finetypes, comprising 132 cases (8%), with a median cluster size of two (range 2–21) and duration of 45 days (range 6–356). Between zero and five clusters were detected yearly. Among 18 cases with known epidemiological links, 14 (78%) were within detected spatiotemporal clusters. CgMLST data from eight clusters supported some clusters but rejected others. Systematic cluster detection using finetype could reveal missed epidemiological links, potentially enabling public health action. However, its impact in preventing additional IMD-B cases is likely limited due to small cluster sizes, though meaningful given the severity of IMD-B. Simple finetype mapping may provide a resource-efficient alternative to SaTScan™.

Introduction: Streptococcus pneumoniae is a major cause of community-acquired pneumonia and invasive diseases. Vaccination prevents pneumococcal disease caused by vaccine serotypes but leads to an increase in disease caused by non-vaccine serotypes. Aim: We aimed to characterise serotype 38 isolates from invasive pneumococcal disease (IPD) patients in Germany, Poland and the Netherlands to explain a recent surge in cases. Methods: IPD surveillance data from 2013/2014 to 2023/2024 were reviewed in all three countries for trends in serotype 38 incidence. Collected isolates were serotyped and phenotypically tested for antimicrobial resistance. Selected serotype 38 isolates (n=130) were sequenced and subjected to phylogenetic analysis, along with 213 publicly available genomes, and characterised according to their virulence and resistance genes. Results: Surveillance data revealed an increase in the percentage of serotype 38 in IPD in Germany and Poland in 2023/2024. This was most pronounced among children aged 0-4 years (from 4.3% to 17.1% and 4.0% to 15.8% of IPD cases, respectively) and adults aged ≥60 years (from 1.5% to 7.0% and from 0.7% to 2.9%, respectively). No such rise in serotype 38 IPD was observed in the Netherlands. Phylogenetic analysis showed that recent isolates mostly emerged from previously circulating strains, showed no significant changes in gene content and carried little antimicrobial resistance genes. Conclusion: The recent surge in non-vaccine serotype 38 among IPD cases in Germany and Poland cannot be explained by changes in antimicrobial resistance or other genetic changes. Our study underscores the importance of international collaboration in monitoring pneumococcal serotype trends, to inform policymakers.

Background: During the COVID-19 pandemic, many countries adopted social distance measures and lockdowns of varying strictness. Social contact patterns are essential in driving the spread of respiratory infections, and country-specific measurements are needed. This study aimed to gain insights into changes in social contacts and behaviour during the early pandemic phase in Norway. Methods: We conducted an online panel study among a nationally representative sample of Norwegian adults by age and gender. The panel study included six data collections waves between April and September 2020, and 2017 survey data from a random sample of the Norwegian population (including children < 18 years old) were used as baseline. The market research company Ipsos was responsible for carrying out the 2020 surveys. We calculated mean daily contacts, and estimated age-stratified contact matrices during the study period employing imputation of child-to-child contacts. We used the next-generation method to assess the relative reduction of R0 and compared the results to reproduction numbers estimated for Norway during the 2020 study period. Results: Over the six waves in 2020, 5 938 observations/responses were registered from 1 718 individuals who reported data on 22 074 contacts. The mean daily number of contacts among adults varied between 3.2 (95%CI 3.0-3.4) to 3.9 (95%CI 3.6–4.2) across the data collection waves, representing a 67–73% decline compared to pre-pandemic levels (baseline). Fewer contacts in the community setting largely drove the reduction; the drop was most prominent among younger adults. Despite gradual easing of social distance measures during the survey period, the estimated population contact matrices remained relatively stable and displayed more inter-age group mixing than at baseline. Contacts within households and the community outside schools and workplaces contributed most to social encounters. Using the next-generation method R0 was found to be roughly 25% of pre-pandemic levels during the study period, suggesting controlled transmission. Conclusion: Social contacts declined significantly in the months following the March 2020 lockdown, aligning with implementation of stringent social distancing measures. These findings contribute valuable empirical information into the social behaviour in Norway during the early pandemic, which can be used to enhance policy-relevant models for addressing future crises when mitigation measures might be implemented.

Background During the COVID-19 pandemic, many countries adopted social distance measures and lockdowns of varying strictness. Social contact patterns are essential in driving the spread of respiratory infections, and country-specific measurements are needed. This study aimed to gain insights into changes in social contacts and behaviour during the early pandemic phase in Norway. Methods We conducted an online survey among a nationally representative sample of Norwegian adults, including six data collections/waves between April and September 2020, and used survey data from 2017 as baseline. We calculated mean daily contacts, and estimated age-stratified contact matrices that were used to estimate reproduction numbers during the study period. Results The mean daily number of contacts varied between 3.2 (95% CI 3.0-3.4) to 3.9 (95% CI 3.6-4.2) across waves, representing a 67-73% decline compared to pre-pandemic levels. Fewer contacts in the community setting largely drove the reduction; the drop was most prominent among younger adults. Despite gradual easing of social distance measures during the survey period, population contact matrices remained relatively stable and displayed more inter-age group mixing than at baseline. Contacts within households and the community outside schools and workplaces contributed most to social encounters. Conclusion Social contacts experienced a significant decline during the months following the March 2020 lockdown in Norway, aligning with the implementation of stringent social distancing measures. The findings contribute valuable empirical information into the social behaviour of the Norwegian population during the early pandemic, which can be used to enhance policy-relevant models for addressing future crises when mitigation measures might be implemented.

COVID-19 control measures have resulted in a decline in invasive bacterial disease caused by Neisseria meningitidis (IMD), Streptococcus pneumoniae (IPD), and Haemophilus influenzae (Hi-D). These species comprise different serogroups and serotypes that impact transmissibility and virulence. We evaluated type- and pathogen-specific changes in invasive bacterial disease epidemiology in the Netherlands during the first year of the SARS-CoV-2 pandemic. Cases were based on nationwide surveillance for five bacterial species with either respiratory (IMD, IPD, Hi-D) or non-respiratory (controls) transmission routes and were compared from the pre-COVID period (April 2015–March 2020) to the first COVID-19 year (April 2020–March 2021). IMD, IPD, and Hi-D cases decreased by 78%, 67%, and 35%, respectively, in the first COVID-19 year compared to the pre-COVID period, although effects differed per age group. Serogroup B-IMD declined by 61%, while serogroup W and Y-IMD decreased >90%. IPD caused by serotypes 7F, 15A, 12F, 33F, and 8 showed the most pronounced decline (≥76%). In contrast to an overall decrease in Hi-D cases, vaccine-preventable serotype b (Hib) increased by 51%. COVID-19 control measures had pathogen- and type-specific effects related to invasive infections. Continued surveillance is critical to monitor potential rebound effects once restriction measures are lifted and transmission is resumed.

The COVID-19 control measures have resulted in a decline in invasive bacterial disease caused by Neisseria meningitidis (IMD), Streptococcus pneumoniae (IPD), and Haemophilus influenzae (Hi-D). The species comprise different serogroups and serotypes that impact transmissibility and virulence. We evaluated type- and pathogen-specific changes in invasive bacterial disease epidemiology in the Netherlands during the first year of the SARS-CoV-2 pandemic. Cases were based on nationwide surveillance for five bacterial species with either respiratory (IMD, IPD, Hi-D) or non-respiratory (controls) transmission routes and compared between the pre-COVID period (April 2015-March 2020) and the first COVID-19 year (April 2020-March 2021). IMD, IPD, and Hi-D cases decreased by 78%, 67%, and 35%, respectively, in the first COVID-19 year compared to the pre-COVID period although effects differed per age group. Serogroup B-IMD declined by 61%, while serogroup W and Y-IMD decreased >90%. IPD caused by serotypes 7F, 15A, 12F, 33F, and 8 showed the most pronounced decline (≥76%). In contrast to an overall decrease in Hi-D cases, vaccine-preventable serotype b (Hib) increased by 51%. COVID-19 control measures had pathogen- and type-specific effects related to invasive infections. Continued surveillance is critical to monitor potential rebound effects once restriction measures are lifted and transmission is resumed.