What's going around in Belgium?

Sciensano combines sentinel GP consultations, sentinel-laboratory positivity, hospital and ICU admissions, wastewater detection of SARS-CoV-2, and variant characterisation into a weekly respiratory-virus picture covering flu, SARS-CoV-2, and RSV. The same indicators feed ECDC ERVISS. On infectrisk.com we condense this picture into a qualitative low/moderate/high classification.

“Tripledemic” is a media term for the simultaneous winter circulation of flu, COVID-19, and RSV first widely discussed during the 2022–2023 season. Belgium saw clear co-circulation of all three pathogens that winter, with notable pressure on paediatric wards from RSV and on adult critical care from flu and COVID-19. Co-circulation has recurred each winter since, though the relative intensity of each pathogen varies.

The drivers are consistent across temperate western Europe. Many respiratory viruses remain stable longer in cold, dry indoor air, and heated indoor environments reduce humidity in ways that weaken airway defence. People mix indoors more during Belgian winters, schools amplify transmission among children, and end-of-year gatherings accelerate spread. Immunity to seasonal strains is also typically at its lowest as exposure rises.

Sciensano uses thresholds derived from historical reference data. Current indicators (sentinel consultations, positivity rates, hospitalisations, wastewater signals) are compared against baselines from past non-epidemic weeks and against reference points from severe past seasons. When several indicators cross into elevated ranges simultaneously, the weekly bulletin flags activity as high. Belgium's ERVISS contribution uses the same framework for cross-country comparison.

Belgium's winter respiratory burden broadly resembles that of the Netherlands, France, and Luxembourg, reflecting similar climate, school calendars, and indoor-contact patterns. Because all these countries report into ECDC ERVISS on the same schedule and methodology, the relative timing and intensity of their peaks is easy to read in the European dashboards. Lead–lag patterns are usually small, driven more by school terms and travel than by climate.