Key Points

• The various waves of COVID-19 since its emergence in France in 2020 should be compared with caution, as surveillance systems are subject to varying performance over time.

• SI-DEP collects all RT-PCR and antigen test results through automated daily data reporting. However, testing strategies and people’s behavior regarding test utilization have evolved over the three years of the pandemic. Furthermore, the high population mobility in the Île-de-France region, with intra-regional, inter-regional, and international travel, impacts the denominators used to calculate virological indicators depending on the time of year.

• Syndromic surveillance provided by the Oscour® and SOS Médecins systems is influenced by the changing number of participating emergency departments and organizations, by coding rates, and by changes in practices and knowledge.

• COVID-19 cases requiring conventional hospitalization or admission to critical care units, as well as deaths in healthcare facilities, were systematically recorded using the SI-VIC® system based on virological or radiological confirmation. This system can be considered robust over time but initially did not adequately document the nature of SARS-CoV-2 infection: reason for hospitalization or comorbidity.

• Virus sequencing data produced by the Emergen consortium, although not exhaustive, contribute to strengthening the surveillance of SARS-CoV-2 variants. They have made it possible to track the emergence and subsequent progression of several variants, often first identified in the Île-de-France region.

• This set of measures has made it possible to describe epidemic trends, track changes in the frequency and severity of the disease, and derive useful parameters for management and forecasting in a region severely affected by COVID-19.

• SARS-CoV-2 will continue to circulate, and its evolution will continue to be monitored by Santé publique France, which will adapt surveillance systems to new knowledge and challenges surrounding this disease, which has become endemic worldwide.