Early COVID-19 vaccine effectiveness of XBB.1.5 vaccine against hospitalization and ICU admission, the Netherlands, 9 October - 5 December 2023 (preprint)

We present early vaccine effectiveness (VE) estimates of the 2023 seasonal COVID-19 vaccination campaign using XBB.1.5 vaccine against COVID-19 hospitalization and ICU admission in previously vaccinated adults [≥]60 years old in the Netherlands. We compared vaccination status of 2050 hospitalizations including 92 ICU admissions with age group-, sex-, region- and date-specific population vaccination coverage between 9 October and 5 December 2023. VE against hospitalization was 70.7% (95% CI: 66.6; 74.3), VE against ICU admission was 73.3% (95% CI: 42.2; 87.6).

Determinants of COVID-19 vaccine uptake in the Netherlands: a nationwide registry-based study (preprint)

By September 2022, uptake of at least one dose of COVID-19 vaccine in the Dutch adult population was 84%. Ecological studies have indicated lower uptake in certain population groups. We aimed to investigate determinants of COVID-19 vaccine uptake in the Netherlands at individual level to evaluate and optimize implementation of the vaccination program and generate hypotheses for research on drivers of and barriers to vaccination. A retrospective database study was performed including the entire Dutch population [≥]18. Vaccination data (5 January 2021 - 18 November 2021) were at individual level linked to sociodemographic data. Random forest analyses ranked sociodemographic determinants of COVID-19 vaccine uptake. The most important determinant was age; uptake increased until the age of 80 (67% in 18-35 years, 92% in 67-79 years and 88% in those >80). Personal income and socioeconomic position ranked second and third, followed by migration status. Uptake was lower among individuals in the lowest income group (69%), receiving social benefits (56%), and individuals with two parents born abroad (59%). Our finding that age is the most important determinant for uptake likely reflects the prioritisation of elderly in the programme and the general understanding of their increased vulnerability. However, our findings also reveal important other disparities in vaccine uptake. How to best address this inequity in future vaccination campaigns requires further research.

Determinants of COVID-19 booster uptake in the Netherlands, Autumn 2022: how well were those at risk for severe disease reached? (preprint)

Background: A booster with bivalent COVID-19 vaccine was offered in the Netherlands in autumn, 2022. We aimed to investigate vaccine uptake during the autumn 2022 booster round among the population subgroups at risk for severe COVID-19 that were specifically targeted by this campaign: the medical risk group aged 18-59 years and individuals [≥]60 years. We calculated booster uptake in both populations and analyzed determinants of booster uptake among those who had received at least one prior COVID-19 vaccination. Methods: Having had an autumn 2022 booster dose was defined as having received a COVID-19 vaccination between 19 September 2022 and 7 March 2023. The study population included individuals who received at least one previous COVID-19 vaccination. National registries of sociodemographic determinants and COVID-19 vaccination were linked by a unique person identifier. Voting proportions for political parties were included at neighborhood level. Determinants of COVID-19 vaccine autumn booster uptake were ranked by importance by random forest analyses. Results: Booster uptake was 68% among those aged [≥]60 and 30% among those aged 18-59 years with a medical risk factor for severe disease. For both target groups the most important determinant for booster uptake was age (15% in 18-29 years to 72% in 80+ years). Voting proportions for progressive liberal political parties ranked second in the random forest analysis in both groups, with an increasing proportion of votes associated with higher uptake. In the 60+ group, household type ranked third, with highest vaccine uptake among married couples without children (72%) and the lowest uptake among unmarried couples with children (47%). In the medical risk group, migration status ranked third. Migrants with two parents born abroad had the lowest uptake (18%), whereas migrants with both parents born in the Netherlands had the highest uptake (35%). Conclusion: Among individuals who had received at least one prior COVID-19 vaccination, the autumn 2022 COVID-19 booster uptake was 68% in people [≥]60 years and 30% in in the medical risk group aged 18-59 years. The most important determinant of booster uptake was age, followed by political preference and household type (60+ group) or migration status (medical risk group). Uptake varied considerably among subgroups in both target groups. Further research should be aimed at understanding the drivers and barriers of vaccine uptake among the subgroups with notably low uptake.