Commonground
Senior Moderator
- Published Date: July 16, 2026
- Issue Date: July 16, 2026
What is already known about this topic?
Human infections with influenza A(H1N2)v viruses of swine origin have been sporadically reported in several countries, usually following direct or indirect exposure to pigs or contaminated environments. However, sustained human-to-human transmission has not yet been documented.
What is added by this report?
This report describes the first laboratory-confirmed human infection with the influenza A(H1N2)v virus in China. Whole-genome sequencing showed that all eight gene segments were closely related to influenza viruses of swine origin circulating in China. No secondary human cases were identified among the close contacts, and no evidence of sustained human-to-human transmission was detected.
What are the implications for public health practice?
This highlights the importance of routine influenza-like illness surveillance, timely whole-genome sequencing, and systematic investigation of unusual influenza A infections. Strengthened surveillance at the human-animal interface and cross-sector collaboration under the One Health framework are essential for early detection and risk assessment of variant influenza viruses.
ABSTRACT
Introduction: Human infections with swine-origin influenza A(H1N2)v viruses have been reported sporadically worldwide, usually following direct or indirect exposure to pigs or contaminated environments. This report describes the first laboratory-confirmed human infection with influenza A(H1N2)v virus in China.
Methods: Following detection of a human infection with influenza A(H1N2)v virus through influenza-like illness surveillance in Yunnan Province in January 2026, an epidemiological investigation, close-contact tracing, animal and environmental sampling, and laboratory testing were conducted. Throat swab specimens were collected for real-time RT-PCR and whole-genome sequencing. Representative influenza virus sequences from the GISAID database were used for sequence comparison and phylogenetic analysis.
Results: A 2-year-old boy presented with fever, cough, and rhinorrhea, and recovered after antiviral, antibacterial, and supportive treatments. Whole-genome sequencing revealed the full-length sequences of all eight gene segments. The virus shared the highest nucleotide homology with swine-origin influenza viruses circulating in China, with nucleotide identities ranging from 95.17% to 98.53%, suggesting a reassortant swine-origin influenza A(H1N2)v virus. Epidemiological investigations revealed no clear history of direct contact with pigs or poultry, although the pigs and poultry were raised near the patient's residence. A total of 47 environmental samples and 28 animal samples were collected during the field investigation. Low viral loads of influenza A virus were detected in some swine and environmental samples; however, full subtyping and sequencing could not be performed for some samples because of low viral loads. Thirty close contacts were traced, and none developed relevant symptoms. No secondary cases or evidence of sustained human-to-human transmission was identified.
Conclusion: This case suggests a sporadic zoonotic transmission event with limited public health risk.
Variant influenza viruses originating from swine represent an ongoing threat to global public health, owing to their genetic diversity and capacity for reassortment (1). When swine influenza viruses infect humans, they are designated with the suffix "v" according to World Health Organization (WHO) nomenclature. According to WHO influenza nomenclature, the suffix "v" is placed outside the subtype parentheses; therefore, the virus described in this report is referred to as influenza A(H1N2)v virus, rather than influenza A(H1N2)v virus. Although most variant influenza infections result in mild illness and limited human-to-human transmission, sporadic zoonotic events underscore the importance of integrated surveillance under the One Health framework (2).
Influenza A(H1N2)v virus has been sporadically reported in several countries and is primarily associated with direct or indirect exposure to pigs. To date, sustained human-to-human transmission has not been documented. In China, swine influenza A(H1N2) viruses have been detected in pig populations, and previous genetic studies have shown that swine influenza viruses circulating in China are genetically diverse and may undergo reassortment among H1N1, H1N2, H3N2, and other swine-origin influenza virus lineages. These findings indicate that swine influenza A virus circulating in domestic pig populations may pose a zoonotic risk. Human infections with A(H1N2)v are rare, and no confirmed cases have been reported in China prior to this event (3). Here, we report the first laboratory-confirmed human infection with A(H1N2)v virus detected through influenza-like illness (ILI) sentinel surveillance in Yunnan Province and describe the comprehensive field investigation and response measures undertaken (4). This case has public health significance because it represents the first recognized human A(H1N2)v infection in China and highlights the value of routine influenza surveillance for detecting rare variant influenza virus infections.
Continued: https://weekly.chinacdc.cn/en/article/doi/10.46234/ccdcw2026.149