The World Health Organization (WHO) was notified about a case of human infection with an influenza A(H5N1) virus on 25 March 2024 by the national authorities of Viet Nam. The patient, who had no underlying medical conditions, developed symptoms on 11 March and died on 23 March. Exposure to birds was ascertained to have taken place in the third week of February. Samples collected from close contacts tested negative for influenza A(H5N1) virus. This is the first human infection with an avian influenza A (H5N1) virus reported in Viet Nam since 2022. According to the International Health Regulations (IHR) 2005, a human infection caused by a novel influenza A virus subtype is an event that has the potential for high public health impact and must be notified to the WHO. Based on available information, WHO assesses the risk to the general population posed by this virus as low.

On 25 March 2024, Viet Nam National Focal Point (NFP) for International Health Regulations (IHR) notified the World Health Organization (WHO) of one case of human infection with an influenza A(H5N1) virus in a 21-year-old male with no underlying conditions from Khanh Hoa Province, Viet Nam.

The case developed a fever and cough on 11 March 2024 and was admitted on 15 March to a local hospital due to persistent symptoms, including abdominal pain and diarrhoea. On 17 March, his condition worsened, and he was transferred to the Intensive Care Unit (ICU) of a provincial hospital. On 20 March, the patient was transferred to another provincial hospital with a diagnosis of severe pneumonia, severe sepsis, and acute respiratory distress syndrome. The case died on 23 March.

On 19 March, samples were taken for real-time polymerase chain reaction (RT-PCR) testing by the Pasteur Institut in Nha Trang, which resulted in a positive result for the influenza (H5) virus. On 22 March, genomic sequencing conducted by the Pasteur Institut of Nha Trang revealed the presence of the avian influenza A (H5N1) virus.

Initial results from the case investigation revealed that during the second and third weeks of February 2024, the case went bird hunting. Between that time and the onset of illness, no contact with dead or sick poultry nor contact with anyone exhibiting similar symptoms was reported. Among close contacts traced, no further cases of influenza A(H5N1) were detected.

Animal influenza viruses normally circulate in animals but can also infect humans. Infections in humans have primarily been acquired through direct contact with infected animals or contaminated environments. Depending on the original host, influenza A viruses can be classified as avian influenza, swine influenza, or other types of animal influenza viruses.

Avian influenza virus infections in humans may cause diseases ranging from mild upper respiratory tract infection to more severe diseases and can be fatal. Conjunctivitis, gastrointestinal symptoms, encephalitis and encephalopathy have also been reported. There have also been several detections of A(H5N1) virus in asymptomatic persons who had exposure to infected birds in the days before a sample was collected.

Laboratory tests are required to diagnose human infection with influenza. WHO periodically updates technical guidance protocols for the detection of zoonotic influenza using molecular methods, e.g. RT-PCR. Evidence suggests that some antiviral drugs, notably neuraminidase inhibitors (oseltamivir, zanamivir), can reduce the duration of viral replication and improve prospects of survival in some cases.

From 2003 to 25 March 2024, a total of 888 worldwide human cases of infection of influenza A(H5N1), including 463 deaths, have been reported to WHO from 23 countries. Almost all cases of human infection with avian influenza A(H5N1) have been linked to close contact with infected live or dead birds, or contaminated environments.

Since 2003, 129 human infections with influenza A (H5N1), including 65 deaths, have been reported in Viet Nam. The most recent avian influenza A (H5) case was reported in October 2022 from Northern Province of Phu Tho, Viet Nam.