COVID-19 hospitalizations in the Netherlands, 2023-2024: disease burden and vaccine effectiveness

Since the cessation of real-time monitoring of COVID-19 hospitalizations in early 2024, the burden of and vaccine effectiveness (VE) against severe COVID-19 in the Netherlands was largely unknown. Recently, hospitalization data from 2024 were made available for the purpose of monitoring and evaluating the COVID-19 vaccination campaigns. These data were linked to the population registry, vaccination registry and healthcare use data (for classification into medical risk groups). We analyzed the number and incidence of COVID-19 hospitalizations in 2023 and 2024 by age and medical risk group. VE against hospitalisation of the autumn booster of 2023 (by time since vaccination, 25 September 2023 to 16 September 2024) and of the autumn booster of 2024 (16 September to 31 December 2024) were estimated by medical risk group among persons aged 60 years and older using Cox proportional hazards models with calendar time as underlying time scale and vaccination status as time-varying exposure. Models were adjusted for age, sex, region and household socio-economic status. From around age 60 onward, intermediate and high medical risk groups had a markedly higher incidence than younger age groups, increasing with age. Persons in the low medical risk group had a low incidence up to the age of 80. In 2024, incidence was lower than in 2023. For both autumn booster rounds, estimated VE against hospitalisation was moderate at 55-67% in the first 3 months post-vaccination. In the high medical risk group, 2023 VE decreased fast and was no longer significant at 6 months post-vaccination. For both years, estimates of the number of averted hospitalizations and number needed to vaccinate to prevent one hospitalization indicated that significant health benefit can be achieved by vaccinating the intermediate and high medical risk groups aged 60 years and older. Efforts to increase the moderate vaccine uptake among risk groups could potentially prevent a considerable disease- and healthcare burden. Highlights- In 2023 and 2024, incidence of COVID-19 hospitalization was highest among medical risk groups aged 60 years and older, despite vaccination campaigns. - Estimated VE against hospitalisation of the 2023 and 2024 autumn booster campaigns was moderate (55-67%) in the first year-quarter post-vaccination among persons aged 60 years and older. - Estimated VE of the 2023 autumn booster decreased over the year, and faster among persons with a medical risk condition. Data availability precluded estimates of 2024 VE beyond the first 3 months since the start of the campaign. - Despite lower and waning VE, the estimated number needed to vaccinate to prevent one COVID-19 hospitalization was much lower among intermediate and high medical risk groups compared with the low medical risk group.