• New human cases {2}:
° From 7 September to 7 October 2026, based on reporting date, detections of influenza A(H5N1) in one human, influenza A(H9N2) in four humans and influenza A(H1N1) variant (A(H1N1)v) in one human were officially reported.
• Circulation of influenza viruses with zoonotic potential in animals:
° High pathogenicity avian influenza (HPAI) events in poultry and non- poultry animal species continue to be reported to the World Organisation for Animal Health (WOAH).{3} The Food and Agriculture Organization of the United Nations (FAO) also provides a global update on avian influenza viruses with pandemic potential.{4} Additionally, low pathogenicity avian influenza viruses as well as swine influenza viruses continue to circulate in animal populations.
• Risk assessment {5}:
° There have been no reports of sustained human-to-human transmission associated with the above-mentioned human infection events. Based on information available at the time of this update, the overall public health risk from currently known influenza A viruses detected at the human-animal interface has not changed and, at present, these viruses are not thought to be capable of sustained human-to-human transmission, although this could change as they evolve. Whilst human infections with viruses of animal origin are infrequent, they are not unexpected at the human-animal interface.
• Risk management:
° Candidate vaccine viruses (CVVs) for zoonotic influenza viruses intended for pandemic preparedness purposes, were reviewed and updated at the September 2026 WHO consultation on influenza vaccine composition for use in the Southern Hemisphere 2027 influenza season. A detailed summary of zoonotic influenza viruses characterized since February 2026 is published and updated CVVs lists are published.
• IHR compliance {6}:
° This includes any influenza A virus that has demonstrated the capacity to infect a human, and its haemagglutinin (HA) gene (or protein) is not a mutated form of those, i.e. A(H1) or A(H3), circulating widely in the human population. Information from these notifications is critical to inform risk assessments for influenza at the human-animal interface.
Avian influenza viruses in humans
° A(H5N1), Cambodia
§ On 27 September 2026, Cambodia notified WHO of a laboratory- confirmed human infection with an avian influenza A(H5N1) virus in an adult male, from Oddar Meanchey Province. He developed a runny nose on 24 September, and respiratory swabs collected that day tested positive for influenza A(H5N1) at the National Institute of Public Health on 26 September. Institut Pasteur du Cambodge, a WHO H5 Reference Laboratory, confirmed the result on 27 September. The patient was admitted to a referral Hospital for isolation, clinical monitoring and oseltamivir treatment. Genomic sequencing of the virus from this case could not be done due to a low viral load.
§ The national and provincial Rapid Response Teams, in collaboration with animal health and local authorities, are conducting epidemiological, environmental and animal health investigations. The patient frequently visited a family member’s poultry farm. At the farm, chickens began becoming ill and dying around 13 September. Poultry specimens collected from remaining birds on 22 September tested positive for avian influenza.
§ Additional specimens were collected for testing from five direct contacts with the case and three persons with poultry exposure and all were negative for influenza A(H5N1). All identified contacts are being monitored for symptoms 14 days.
§ This is the sixth case reported in Cambodia in 2026.
§ According to reports received by WOAH, various influenza A(H5) subtypes continue to be detected in wild and domestic birds in Africa, the Americas, Asia, Europe and Oceania. Infections in non-human mammals are also reported, including in marine and land mammals.{7} A list of bird and mammalian species affected by HPAI A(H5) viruses is maintained by FAO.{8}
° Risk assessment for avian influenza A(H5N1) viruses:
1. What is the current global public health risk of additional human cases of infection with avian influenza A(H5N1) viruses?
§ Most human infections so far have been reported in people exposed to A(H5N1) viruses, for example, through contact with infected poultry or contaminated environments, including live poultry markets, and occasionally infected mammals and contaminated environments. As long as the viruses continue to be detected in animals and related environments humans are exposed to, further human cases associated with such exposures are expected but remain unusual.
§ The impact for public health if additional sporadic cases are detected is minimal.
§ The current overall global public health risk is low.
2. What is the likelihood of sustained human-to-human transmission of avian influenza A(H5N1) viruses related to the events above?
§ No sustained human-to-human transmission has been identified associated with the recent reported human infections with avian influenza A(H5N1) viruses. There has been no reported human-tohuman transmission of A(H5N1) viruses since 2007, although there may be gaps in investigations. In 2007 and the years prior, small clusters of A(H5N1) virus infections in humans were reported, including some involving health care workers, where limited human-to-human transmission could not be excluded; however, sustained human- to-human transmission was not reported.
§ Current evidence suggests that influenza A(H5N1) viruses related to these events did not acquire the ability to efficiently transmit between people.
3. What is the likelihood of international spread of avian influenza A(H5N1) viruses by travellers?
§ Should infected individuals from affected areas travel internationally, their infection may be detected in another country during travel or after arrival. If this were to occur, further community-level spread is considered unlikely as current evidence suggests these viruses have not acquired the ability to transmit easily among humans.
° A(H9N2), China
§ Between 9 and 30 September 2026, China notified WHO of four laboratory-confirmed human cases of A(H9N2) virus infection.
[Age - Province - Symptom onset]
1} < 5-year-old - Henan - 30 August 2026
2} < 5-year-old - Guangdong - 7 September 2026
3} Adult - Henan - 17 September 2026
4)} < 5-year-old - Guizhou - 20 September 2026
§ Three of the cases with mild symptoms were detected in influenza-like illness surveillance and have recovered. The adult has underlying chronic conditions and was still in hospital at the time of reporting.
§ All cases had direct or indirect exposure to poultry and/or local live bird markets. Samples from environments associated with the likely area of exposure of some of the cases tested positive for A(H9) viruses.
§ No further cases were detected among contacts of these cases.
° Risk assessment for avian influenza A(H9N2):
1. What is the global public health risk of additional human cases of infection with avian influenza A(H9N2) viruses?
§ Most human cases follow exposure to the A(H9N2) virus through contact with infected poultry or contaminated environments. Most human infections of A(H9N2) to date have resulted in mild clinical illness. Since the virus is endemic in poultry in multiple countries in Africa and Asia, additional human cases associated with exposure to infected poultry or contaminated environments are expected but remain unusual. The impact to public health if additional sporadic cases are detected is minimal. The overall global public health risk is low.
2. What is the likelihood of sustained human-to-human transmission of avian influenza A(H9N2) viruses related to these events?
§ At the present time, no sustained human-to-human transmission has been identified associated with the recently reported human infections with A(H9N2) viruses. Current evidence suggests that A(H9N2) viruses from these cases did not acquire the ability of sustained transmission among humans.
3. What is the likelihood of international spread of avian influenza A(H9N2) virus by travellers?
§ Should infected individuals from affected areas travel internationally, their infection may be detected in another country during travel or after arrival. If this were to occur, further community level spread is considered unlikely as current evidence suggests the A(H9N2) virus subtype has not acquired the ability to transmit easily among humans. Swine influenza viruses in humans
° Influenza A(H1N1)v, Brazil
§ On 30 September 2026, Brazil notified PAHO/WHO of a laboratory- confirmed human infection with an influenza A(H1N1)v virus in an adult woman, with pre-existing chronic conditions, residing in the state of Santa Catarina. She developed symptoms of influenza-like illness on 16 July 2026 and sought medical attention on 20 July. Her husband and three adult children, who live in the same household, also experienced symptoms of an influenza-like illness; at that time, all were diagnosed, based solely on clinical examination, with a viral infection and received treatment. The woman, however, did not recover. On 27 July, the patient was hospitalized due to worsening respiratory symptoms. She received treatment, including the antiviral oseltamivir, and required intensive care, including ventilatory support. Despite intensive care, the patient passed away on 28 August.
§ A nasopharyngeal sample, collected on 29 July, tested positive for influenza A on 30 July and was subsequently subtyped as influenza A(H1N1) on 31 July. The sample was sent to the reference laboratory for respiratory viruses at the Oswaldo Cruz Institute (IOC/Fiocruz) in Rio de Janeiro for further characterization. On 4 September, genomic analysis identified an influenza A(H1N1)v virus.
§ According to information gathered during an epidemiological investigation conducted by municipal and state teams between 5 and 9 September, the patient had no history of travel or direct contact with swine. However, a possible indirect exposure to swine was identified through a neighbour who raises these animals for personal consumption.
§ Since 2015, twelve cases of human infection with swine-origin virus variants, including this one, have been detected within Brazil’s respiratory virus surveillance workflow.
° Risk Assessment:
1. What is the public health risk of additional human cases of infection with swine influenza viruses?
§ Swine influenza viruses circulate in swine populations in many regions of the world. Depending on geographic location, the genetic characteristics of these viruses differ. Most human cases are exposed to swine influenza viruses through contact with infected animals or contaminated environments. Human infection tends to result in mild clinical illness in most cases. Since these viruses continue to be detected in swine populations, further human cases are expected but remain unusual. The impact for public health if additional cases are detected is minimal. The overall risk of additional human cases is low.
2. What is the likelihood of sustained human-to-human transmission of swine influenza viruses?
§ No sustained human-to-human transmission was identified associated with the event described above. Current evidence suggests that contemporary swine influenza viruses have not acquired the ability of sustained transmission among humans, therefore sustained human-to-human transmission is thus currently considered unlikely.
3. What is the likelihood of international spread of swine influenza viruses by travelers?
§ Should infected individuals from affected areas travel internationally, their infection may be detected in another country during travel or after arrival. If this were to occur, further community level spread is considered unlikely as current evidence suggest that these viruses have not acquired the ability to transmit easily among humans.
For more information on zoonotic influenza viruses, see the report from the WHO Consultation on the Composition of Influenza Virus Vaccines for Use in the Southern Hemisphere Influenza Season that was held on 21-24 September 2026 at this link.
Overall risk management recommendations:
° Surveillance and investigations
• Due to the constantly evolving nature of influenza viruses, WHO continues to stress the importance of global strategic surveillance in animals and humans to detect virologic, epidemiologic and clinical changes associated with circulating influenza viruses that may affect human (or animal) health. Continued vigilance is needed within affected and neighbouring areas to detect infections in animals and humans. Close collaboration with the animal health and environment sectors is essential to understand the extent of the risk of human exposure and to prevent and control the spread of animal influenza. WHO has published guidance on surveillance for human infections with avian influenza A(H5) viruses.
• Epidemiologic and virologic surveillance and the follow-up of suspected human cases should continue systematically. Guidance on investigation of non-seasonal influenza and other emerging acute respiratory diseases has been published on the WHO website.
• Countries should increase avian influenza surveillance in domestic and wild birds, enhance surveillance for early detection in cattle populations in countries where HPAI is known to be circulating, include HPAI as a differential diagnosis in non-avian species, including cattle and other livestock populations, with high risk of exposure to HPAI viruses; monitor and investigate cases in non-avian species, including livestock, report cases of HPAI in all animal species, including unusual hosts, to WOAH and other international organizations, share genetic sequences of avian influenza viruses in publicly available databases, implement preventive and early response measures to break the HPAI transmission cycle among animals through movement restrictions of infected livestock holdings and strict biosecurity measures in all holdings, employ good production and hygiene practices when handing animal products, and protect persons in contact with suspected/infected animals. {7} More guidance can be found from WOAH and FAO.
• When there has been human exposure to a known outbreak of an influenza A virus in domestic poultry, wild birds or other animals – or when there has been an identified human case of infection with such a virus – enhanced surveillance in potentially exposed human populations becomes necessary. Enhanced surveillance should consider the health care seeking behaviour of the population, and could include a range of active and passive health care and/or communitybased approaches, including: enhanced surveillance in local influenza- like illness (ILI)/SARI systems, active screening in hospitals and of groups that may be at higher occupational risk of exposure, and inclusion of other sources such as traditional healers, private practitioners and private diagnostic laboratories.
• Vigilance for the emergence of novel influenza viruses with pandemic potential must be maintained at all times, including during a non- influenza emergency. To maximize the value of influenza surveillance platform for other respiratory threats, WHO has updated and published practical guidance for integrated surveillance.
° Notifying WHO
• All human infections caused by a new subtype of influenza virus are notifiable under the International Health Regulations (IHR, 2005).{8,9} State Parties to the IHR (2005) are required to immediately notify WHO of any laboratory-confirmed {10} case of a recent human infection caused by an influenza A virus with the potential to cause a pandemic {11}. Evidence of illness is not required for this report. Evidence of illness is not required for this report.
• WHO published the case definition for human infections with avian influenza A(H5) virus requiring notification under IHR (2005): https://www.who.int/teams/global-influenzaprogramme/avian-influenza/case-definitions.
° Virus sharing and risk assessment
• It is critical that these influenza viruses from animals or from humans are fully characterized in appropriate animal or human health influenza reference laboratories. Under WHO’s Pandemic Influenza Preparedness (PIP) Framework, Member States are expected to share influenza viruses with pandemic potential on a timely basis {12} with a WHO Collaborating Centre for influenza of GISRS. The viruses are used by the public health laboratories to assess the risk of pandemic influenza and to develop candidate vaccine viruses.
• The Tool for Influenza Pandemic Risk Assessment (TIPRA) provides an in-depth assessment of risk associated with some zoonotic influenza viruses – notably the likelihood of the virus gaining human-to-human transmissibility, and the impact should the virus gain such transmissibility. TIPRA maps relative risk amongst viruses assessed using multiple risk elements. The results of TIPRA complement those of the risk assessment provided here, and those of prior TIPRA risk assessments are published at http://www.who.int/teams/global-influenza-programme/avianinfluenza/tool-for-influenza-pandemic-risk-assessment-(tipra).
° Risk reduction
• Given the observed extent and frequency of avian influenza in poultry, wild birds and some wild and domestic mammals, the public should avoid contact with animals that are sick or dead from unknown causes, including wild animals, and should report dead birds and mammals or request their removal by contacting local wildlife or veterinary authorities.
• Eggs, poultry meat and other poultry food products should be properly cooked and properly handled during food preparation. Due to the potential health risks to consumers, raw milk should be avoided. WHO advises consuming pasteurized milk. If pasteurized milk isn’t available, heating raw milk until it boils makes it safer for consumption.
• WHO has published practical interim guidance to reduce the risk of infection in people exposed to avian influenza viruses.
° Trade and travellers
• WHO advises that travellers to countries with known outbreaks of animal influenza should avoid farms, contact with animals in live animal markets, entering areas where animals may be slaughtered, or contact with any surfaces that appear to be contaminated with animal excreta. Travelers should also wash their hands often with soap and water. All individuals should follow good food safety and hygiene practices.
• WHO does not advise special traveller screening at points of entry or restrictions with regards to the current situation of influenza viruses at the human-animal interface. For recommendations on safe trade in animals and related products from countries affected by these influenza viruses, refer to WOAH guidance.
Links:
° WHO Human-Animal Interface web page https://www.who.int/teams/global-influenza-programme/avian-influenza
° WHO Influenza (Avian and other zoonotic) fact sheet https://www.who.int/news-room/fact-sheets/detail/influenza-(avian-and-other-zoonotic)
° Global framework to accelerate action on avian influenza https://iris.who.int/handle/10665/387613
° WHO Protocol to investigate non-seasonal influenza and other emerging acute respiratory diseases https://www.who.int/publications/i/item/WHO-WHE-IHM-GIP-2018.2
° WHO Public health resource pack for countries experiencing outbreaks of influenza in animals: https://www.who.int/publications/i/item/9789240076884
° Cumulative Number of Confirmed Human Cases of Avian Influenza A(H5N1) Reported to WHO https://www.who.int/teams/global-influenza-programme/avian-influenza/avian-a-h5n1-virus
° Avian Influenza A(H7N9) Information https://www.who.int/teams/global-influenza-programme/avian-influenza/avian-influenza-a-(h7n9)-virus
° World Organisation of Animal Health (WOAH) web page: Avian Influenza https://www.woah.org/en/home/
° Food and Agriculture Organization of the United Nations (FAO) webpage: Avian Influenza https://www.fao.org/animal-health/avian-flu-qa/en/
° WOAH/FAO Network of Expertise on Animal Influenza (OFFLU) http://www.offlu.org/
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{1} This summary and assessment covers information confirmed during this period and may include information received outside of this period.
{2} For epidemiological and virological features of human infections with animal influenza viruses not reported in this assessment, see the reports on human cases of influenza at the human-animal interface published in the Weekly Epidemiological Record here.
{3} Avian influenza. Global situation. World Organisation for Animal Health (WOAH) (https://www.woah.org/en/disease/avian-influenza/#ui-id-2).
{4} Global Avian Influenza Viruses with Zoonotic Potential situation update. Food and Agriculture Organization of the United Nations (FAO) (https://www.fao.org/animal-health/situation-updates/global-aiv-with-zoonoticpotential).
{5} Rapid risk assessment of acute public health events. World Health Organization; 2012 (https://iris.who.int/handle/10665/70810).
{6} Case definitions for the four diseases requiring notification in all circumstances under the International Health Regulations (2005). World Health Organization; 2009 (https://www.who.int/publications/m/item/casedefinitions-for-the-four-diseases-requiring-notification-to-who-in-all-circumstances-under-the-ihr-(2005)).
{7} World Organisation for Animal Health. Statement on High Pathogenicity Avian Influenza in Cattle, 6 December 2024 (https://www.woah.org/en/high-pathogenicity-avian-influenza-hpai-in-cattle/).
{8} World Health Organization. International Health Regulations (2005), as amended through resolutions WHA67.13 (2014), WHA75.12 (2022), and WHA77.17 (2024) (https://apps.who.int/gb/bd/pdf_files/IHR_2014-2022-2024-en.pdf).
{9} World Health Organization. Case definitions for the four diseases requiring notification in all circumstances under the International Health Regulations (2005) (https://www.who.int/publications/m/item/casedefinitions-for-the-four-diseases-requiring-notification-to-who-in-all-circumstances-under-the-ihr-(2005)).
{10} World Health Organization. Manual for the laboratory diagnosis and virological surveillance of influenza (2011) (https://apps.who.int/iris/handle/10665/44518).
{11} World Health Organization. Pandemic influenza preparedness framework for the sharing of influenza viruses and access to vaccines and other benefits, 2nd edition (https://iris.who.int/handle/10665/341850).
{12} World Health Organization. Operational guidance on sharing influenza viruses with human pandemic potential (IVPP) under the Pandemic Influenza Preparedness (PIP) Framework (2017) (https://apps.who.int/iris/handle/10665/259402)
Source:
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