Influenza, commonly known as the flu, is an infectious disease caused by influenza viruses. Four types exist: A, B, C, and D, with types A and B circulating in humans and causing seasonal epidemics. Influenza A virus is widely distributed across aquatic birds, humans, pigs, and other mammals, while influenza B and C viruses primarily infect humans [4].
Disease overview
Influenza
流行性感冒
Evidence-backed informationEN 5/7 applicable sections · ZH 5/7 applicable sectionsUpdated Sep 3, 2026
Influenza is an infectious respiratory disease caused by influenza viruses that circulates worldwide as seasonal epidemics and is preventable through vaccination and non-pharmaceutical measures. Antiviral medications, particularly neuraminidase inhibitors and baloxavir, can reduce the incidence of symptomatic influenza when used for post-exposure prophylaxis and treatment [1][2][3][4]. Annual vaccination remains the cornerstone of prevention, with effectiveness varying by age group, vaccine type, and season [2][3].
Read the full clinical and epidemiological profile6
Symptoms range from mild to severe and commonly include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. Symptoms typically begin one to four days after exposure and last about two to eight days, with diarrhea and vomiting occurring more frequently in children. Complications can include pneumonia, acute respiratory distress syndrome, meningitis, encephalitis, and worsening of pre-existing conditions such as asthma and cardiovascular disease [2][4].
Influenza imposes a substantial burden on community respiratory health, with children facing heightened risks of hospitalization and mortality during circulation periods [2]. The pathogen drives recurring seasonal epidemics and acute outbreaks, prompting public health authorities to implement structured intervention phases to limit spread and protect vulnerable populations [4].
Influenza viruses are primarily transmitted through respiratory droplets produced by coughing and sneezing, with additional transmission occurring via aerosols and contact with virus-contaminated surfaces. Frequent hand washing, respiratory hygiene, and mask use reduce transmission risk [1][4].
Annual vaccination is the primary prevention strategy, recommended for all eligible individuals beginning at six months of age without medical contraindications. When vaccines and antivirals are limited, non-pharmaceutical interventions such as hand and respiratory hygiene, self-isolation of symptomatic individuals, face mask use by patients and caregivers, surface disinfection, rapid testing, contact tracing, and social distancing measures including school closures and travel restrictions are endorsed for outbreak control. Antiviral post-exposure prophylaxis with zanamivir, oseltamivir, laninamivir, and baloxavir probably achieves important reductions in symptomatic influenza among those at high risk [1][2][3][4].
- 1Zhao Y et al. Antivirals for post-exposure prophylaxis of influenza: a systematic review and network meta-analysis. Lancet. 2024 Aug 24. PMID: 39181596. doi: 10.1016/S0140-6736(24)01357-6.PubMed: https://pubmed.ncbi.nlm.nih.gov/39181596/
- 2Committee on Infectious Diseases et al. Recommendations for Prevention and Control of Influenza in Children, 2024-2025: Policy Statement. Pediatrics. 2024 Oct 1. PMID: 39183669. doi: 10.1542/peds.2024-068507.PubMed: https://pubmed.ncbi.nlm.nih.gov/39183669/
- 3Osterholm MT et al. Efficacy and effectiveness of influenza vaccines: a systematic review and meta-analysis. Lancet Infect Dis. 2012 Jan. PMID: 22032844. doi: 10.1016/S1473-3099(11)70295-X.PubMed: https://pubmed.ncbi.nlm.nih.gov/22032844/
- 4Wikipedia contributors. Influenza - Wikipedia [Internet]. Wikipedia. cited 3 Sept 2026.Available from: https://en.wikipedia.org/wiki/Influenza
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Research Radar
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Literature links are provided for discovery and do not alter or validate the surveillance series above.
Data access
Page dataset index with source links and update metadata.
Official sourcesAuthority, cadence, notes83
Australia NINDSS
Australia
Australian national notifiable diseases surveillance dashboard.
Australia NINDSS — Australian Capital Territory
Australian Capital Territory, Australia
Australian NINDSS monthly state/territory notifications for Australian Capital Territory, kept separate from the Australia national aggregate.
Australia NINDSS — New South Wales
New South Wales, Australia
Australian NINDSS monthly state/territory notifications for New South Wales, kept separate from the Australia national aggregate.
Australia NINDSS — Northern Territory
Northern Territory, Australia
Australian NINDSS monthly state/territory notifications for Northern Territory, kept separate from the Australia national aggregate.
Australia NINDSS — Queensland
Queensland, Australia
Australian NINDSS monthly state/territory notifications for Queensland, kept separate from the Australia national aggregate.
Australia NINDSS — South Australia
South Australia, Australia
Australian NINDSS monthly state/territory notifications for South Australia, kept separate from the Australia national aggregate.
Australia NINDSS — Tasmania
Tasmania, Australia
Australian NINDSS monthly state/territory notifications for Tasmania, kept separate from the Australia national aggregate.
Australia NINDSS — Victoria
Victoria, Australia
Australian NINDSS monthly state/territory notifications for Victoria, kept separate from the Australia national aggregate.
Australia NINDSS — Western Australia
Western Australia, Australia
Australian NINDSS monthly state/territory notifications for Western Australia, kept separate from the Australia national aggregate.
Canada PHAC CNDSS Annual
Canada
Canada is the national jurisdiction; subdivision feeds are registered separately.
Switzerland FOPH IDD
Switzerland
Switzerland FOPH/BAG IDD mandatory reporting API normalized to national case rows. Monthly series may use the dashboard CHFL aggregate where CH-only monthly series are not exposed.
China CDC Weekly
China
Monthly notifiable infectious disease reports published by China CDC.
National Disease Control and Prevention Administration
China
Official China public health bulletin and query portal.
PubMed
China
Biomedical literature discovery feed used as supplementary context.
Public Health Science Data Center
Anhui, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Anhui, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Beijing, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Beijing, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Chongqing, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Chongqing, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Fujian, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Fujian, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Guangdong, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Guangdong, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Gansu, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Gansu, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Guangxi, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Guangxi, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Guizhou, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Guizhou, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Henan, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Henan, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Hubei, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Hubei, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Hebei, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Hebei, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Hainan, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Hainan, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Heilongjiang, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Heilongjiang, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Hunan, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Hunan, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Jilin, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Jilin, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Jiangsu, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Jiangsu, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Jiangxi, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Jiangxi, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Liaoning, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Liaoning, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Inner Mongolia, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Inner Mongolia, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Ningxia, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Ningxia, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Qinghai, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Qinghai, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Sichuan, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Sichuan, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Shandong, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Shandong, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Shanghai, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Shanghai, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Shaanxi, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Shaanxi, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Shanxi, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Shanxi, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Tianjin, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Tianjin, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Xinjiang, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Xinjiang, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Tibet, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Tibet, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Yunnan, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Yunnan, China
Province-level statutory infectious disease report published by the responsible health authority.
Public Health Science Data Center
Zhejiang, China
Chinese province-level historical monthly observations; this higher-priority source overlays overlapping official monthly reports.
Provincial statutory infectious disease monthly report
Zhejiang, China
Province-level statutory infectious disease report published by the responsible health authority.
Finland THL Infectious Diseases Register
Finland
Finland THL Infectious Diseases Register national monthly case counts. The current month is ingested as provisional and the latest three months are refreshed for source revisions.
Iceland Directorate of Health Annual Dashboard
Iceland
National annual case notifications by disease. Published values can be revised retrospectively and remain annual period totals.
Iceland Directorate of Health STI Dashboard
Iceland
Monthly STI diagnosis facts from laboratory and registry surveillance; the official dashboard is published on a quarterly schedule.
Iceland Directorate of Health Respiratory Dashboard
Iceland
ISO-week respiratory diagnosis counts. Hospitalizations, samples, and vaccination indicators are separate measures and are not counted as diagnoses.
Iceland Directorate of Health Historical Registry
Iceland
Historical official registry tables for 1997–2021, with annual totals and disease-specific monthly notification facts retained at source grain.
Iceland Directorate of Health Legacy ICD Monthly
Iceland
Historical Saga EHR ICD encounter counts for 1997–2020. This clinical measure is non-comparable with registry notifications and is kept separate.
JP NIID Weekly
Japan
Japan weekly infectious disease surveillance via NIID/JIHS.