Vietnam Reports First Human H5N1 Avian Flu Case of 2025

HO CHI MINH CITY, Vietnam — Health officials in Vietnam have confirmed an 8-year-old girl has contracted a severe H5N1 avian flu infection, marking the first recorded human case of 2025. The patient from Tay Ninh province is exhibiting encephalitis symptoms, as reported in a statement from the Ho Chi Minh City Department of Health on April 18.

The girl’s symptoms began on April 11, characterized by fever, headache, and vomiting. Initially admitted to a provincial hospital, she was transferred to Children’s Hospital in Ho Chi Minh City on April 13 after her condition failed to improve. There, doctors diagnosed her with encephalitis.

Officials noted that the child has an underlying heart condition and underwent surgery for a ventricular septal defect at just 2 months old. Polymerase chain reaction tests on her respiratory samples came back negative for H5 avian flu, but a cerebrospinal fluid sample confirmed the presence of the virus. These results were verified by the Pasteur Institute in Ho Chi Minh City.

The patient remains on a ventilator, with her vital signs currently stable, according to health authorities.

An epidemiological investigation revealed the child had contact with a poultry flock at her grandmother’s house, which experienced mass deaths two weeks before she fell ill. Officials caution that H5N1 infections primarily affecting the central nervous system are rare, although there have been precedents. In one documented case, two siblings showed severe neurologic symptoms without respiratory distress, indicating a broader spectrum of illness than previously recognized.

The last recorded human case of H5N1 in Vietnam involved an 18-year-old man from Long An province, who exposed himself to sick poultry and subsequently died from the infection.

It is currently unclear which H5N1 clade is responsible for the girl’s infection. However, in 2024, scientists warned of a reassortant strain of H5N1 circulating in the Greater Mekong region that has affected both birds and humans. This strain combines surface proteins from an older clade (2.3.2.1c) that has circulated in parts of Asia with a newer clade (2.3.4.4b) that has been spreading globally since 2022.