Novel influenza A

人感染新亚型流感

Evidence-backed information EN 5/7 applicable sections · ZH 5/7 applicable sections Updated Oct 23, 2026

Novel influenza A refers to zoonotic infections with non-human-origin influenza A viruses that have acquired or threaten to acquire the capacity for efficient human-to-human transmission, representing the antecedent stage of pandemic emergence ^[1]. These infections occur sporadically through cross-species transmission from avian or swine reservoirs and pose persistent pandemic threats ^[2]. The viruses originate from antigenically diverse wild aquatic bird populations, where infection is typically asymptomatic, but may adapt to human hosts through species-specific molecular interactions governing tropism and transmission ^[1].

Read the full clinical and epidemiological profile 6

Definition

Novel influenza A denotes infection by an influenza A virus of non-human origin (typically avian or swine) that has crossed into human populations and may be adapting toward sustained human-to-human transmission ^[1]. Such a virus becomes capable of initiating an influenza pandemic when it achieves efficient replication and transmissibility within the new human host ^[1].

Clinical features

The clinical presentation of zoonotic and early-pandemic novel influenza A infections generally resembles that of seasonal influenza, with abrupt onset of respiratory symptoms and myalgia, with or without fever, and most patients recovering within approximately one week; however, some individuals may experience severe or fatal complications ^[2].

Epidemiology

Novel influenza A infections occur sporadically as zoonotic spillover events from animal reservoirs rather than as sustained seasonal circulation, and the global burden of seasonal influenza (caused by influenza A and B) declined markedly in 2020–21 following the emergence of SARS-CoV-2 and partially rebounded in 2021–22 ^[2]. The vast antigenic reservoir of influenza A in wild aquatic birds provides an ongoing source of sporadic zoonotic introductions of avian or swine origin, each of which constitutes a potential pandemic threat ^[2].

Transmission

Sporadic zoonotic transmission occurs when avian or swine influenza A viruses cross species barriers from animal reservoirs into humans; pandemic emergence requires that a virus acquire sufficient adaptive mutations to support stable human-to-human transmission ^[1]. The transition is governed by species-specific virus–host cell interactions that determine tropism, including binding, entry, nuclear replication, assembly, and release of virions ^[1].

Prevention

Prevention of novel influenza A relies on broad seasonal influenza vaccination programmes to reduce the burden of circulating influenza viruses and on continued vigilance for zoonotic spillover events that could seed a pandemic ^[2]. The development of next-generation vaccines with improved effectiveness, together with targeted antivirals and therapeutic agents informed by an understanding of viral tropism, is a central component of preparedness against emerging novel influenza A strains ^[1]^[2].

References

1 AbuBakar U et al. Avian Influenza Virus Tropism in Humans. Viruses. 2023 Mar 24. PMID: 37112812. doi: 10.3390/v15040833. PubMed: https://pubmed.ncbi.nlm.nih.gov/37112812/
2 Uyeki TM et al. Influenza. Lancet. 2022 Aug 27. PMID: 36030813. doi: 10.1016/S0140-6736(22)00982-5. PubMed: https://pubmed.ncbi.nlm.nih.gov/36030813/