Headlines - Preliminary Report on the Flu Outbreak in France (2017–2018 Season)

The flu season started early this year. It began in the Île-de-France region in week 49 of 2017 (December 4–10) and spread to all metropolitan regions within four weeks. The epidemic had ended in all metropolitan regions by the end of March, in week 13. It was exceptionally long, lasting a total of 16 weeks. The scale of the epidemic was moderate in outpatient care, with an estimated 2.4 million visits for flu-like illness. Outpatient visits for influenza-like illness were more frequent among children, with a cumulative incidence rate of 8,187 per 100,000 among those under 5 years of age and 5,471 per 100,000 among those aged 5–14. This rate was lower among those aged 15–64 (3,465 per 100,000) and those aged 65 and older (1,324 per 100,000).The decrease in influenza activity observed among children under 15 years of age in week 01/2018 is likely related to the end-of-year school holidays, due to reduced virus transmission in school settings. A second peak of activity, less intense than the first, was observed in week 02 among children under 5 and in week 03 among those aged 5–14. The number of hospitalizations for influenza (9,738 hospitalizations) during this epidemic is the highest since 2009–2010. It is significantly higher than during the 2016–2017 (6,500 hospitalizations) and 2014–2015 (3,400 hospitalizations) epidemics. Among these hospitalized patients, 20% were under 5 years of age and 53% were 65 years of age and older.The number of severe influenza cases admitted to intensive care and reported to Santé publique France is the highest since the 2009-2010 season, when this surveillance system was established: 2,915 cases since November 1, 2017. Two peaks were also observed: the first in week 01 (449 cases) and a second, less intense peak between weeks 07 and 10. In outpatient settings, 1,600 influenza viruses were detected in the 2,749 samples analyzed (58%) since week 40. Of these, 48% were type B viruses (98% of which were of the Yamagata lineage), 44% were A(H1N1)pdm09 viruses, and 8% were A(H3N2) viruses. In hospitals, 52% of the 23,537 influenza viruses detected were type A and 48% were type B.During the 16 weeks of the epidemic, a significant excess mortality from all causes was observed in metropolitan France. The estimate of excess mortality, calculated based on a sample of 3,000 municipalities and extrapolated to the national level, is 17,900 deaths over this period.Based on a statistical model developed by Santé publique France, the excess mortality attributable to influenza is estimated at 73%, or approximately 13,000 deaths across all age groups. Of these deaths, 93% involved people aged 65 and older.As of February 28, 2018, vaccination coverage across all programs is estimated at 45.6%, stable compared to the 2016–2017 season (45.7% as of February 28, 2017). It is estimated at 50% among those aged 65 and older and at 28.7% among at-risk individuals under 65.