The COVID-19 pandemic underlined the vulnerability of the nursing home (NH) population, which accounted for about 50% of all COVID-related deaths in Belgium. In October 2022, a NH-based sentinel surveillance to monitor influenza-like illness (ILI) was set up to complement initiatives in the general population. This study aims to report the main findings of the past three ILI seasons in NH.

The surveillance is organised in two components. In the epidemiological component, the number of new ILI-cases, hospital admissions and deaths are reported weekly. In the virological component, a maximum of two samples are sent weekly to the National Reference Centre (NRC) for Influenza, during the influenza surveillance season. The samples are analysed for SARS-CoV-2, influenza, and 16 other respiratory infections. Recruitment and follow-up are organised through the regional authorities regulating Infection Prevention and Control in NH.

In Belgium, there are about 1,559 NH and 151,130 residents. In 2022-23, 2023-24, and 2024-25, 34 (2,943 residents), 41 (3,834 residents), and 70 NH (6,925 residents) participated during the entire season, respectively. In the first and second seasons, there were disproportionately more participating NH in Flanders. There were peaks of ILI per 1,000 NH residents in December 2022 (20), December 2023 (20), February 2024 (16), and January 2025 (23) (Figure 1). In February 2023, an increase in ILI, caused by an outbreak in one NH, could be observed. The highest ILI incidence was reported in January 2025. A limited number of samples (237) were received over the three seasons. Most detected viruses were SARS-CoV-2 (10), enterovirus/rhinovirus (15) and enterovirus/rhinovirus (11) in season 2022-23, 2023-24, and 2024-25, respectively.

The peak of ILI per 1,000 NH residents coincided with that of the influenza epidemic in all seasons, highlighting that this surveillance complements those already established in the general population and enables the federal Risk Assessment Group to propose essential mitigation measures to the authorities. Gradually setting up a NH-based surveillance proved effective in Belgium, resulting in a robust sentinel network. The virological component requires revision due to the limited number of samples received.