Key points

Acute Respiratory Infections (ARI)

• A season characterized by two successive peaks: one in late December, linked to the bronchiolitis outbreak and COVID-19, and another in late January, due to the flu outbreak.

• A season marked by the co-circulation of multiple respiratory pathogens other than the usual viruses: an unusual increase in Mycoplasma pneumoniae infections starting in the fall (see update as of March 24, 2024) and a resurgence of pertussis cases since the beginning of 2024 (see regional update as of September 5, 2024).

Bronchiolitis

• An epidemic that began earlier than before the COVID-19 pandemic, but was shorter and less intense than in 2022–2023

  • Before the Covid-19 pandemic, the transition to the epidemic phase of bronchiolitis usually occurred around week 47 or 48 (late November); in 2023–2024, it began in week 44 (early November).

  • Lasting 6 to 11 weeks before the arrival of SARS-CoV-2, the last two epidemic seasons were marked by a prolonged circulation of RSV, lasting 13 to 14 weeks. In 2023–2024, the duration is similar to that before the COVID-19 pandemic (11 epidemic weeks).

• A season of moderate intensity compared to previous years.

Influenza

• A typical epidemic lasting from mid-December to late February, or 11 weeks. A single wave with an epidemic peak in week S04-2024 or S05-2024, depending on the data source.

• The level of healthcare utilization indicators was relatively similar to the previous season, except for hospitalizations, which were slightly higher.

• Circulation of the A(H1N1)pdm09 virus was predominant nationwide.

• Regional vaccination coverage was estimated at 46.7% among at-risk individuals targeted for vaccination, and 53.0% among those aged 65 and older, lower than in 2022–2023.

COVID-19

• Persistent circulation of SARS-CoV-2 throughout the year. Two resurgences of Covid-19 during periods of influenza and bronchiolitis epidemics

  • Increase in indicators starting in July 2023 with two peaks, in September and December.

  • Decrease observed during the month of December (week varies by source) and indicators remaining at low levels between mid-February and early June.

• Peak share of hospitalizations in December (3.7% in S50-2023).

• Co-circulation of Omicron recombinants during the second half of 2023, followed by the JN.1 variant (and its sublineages) becoming the dominant strain starting in December 2023.

• Vaccination coverage estimated at 27.9% among people aged 65 and older following the vaccination campaign from October 2023 to February 2024.