Bird Flu Pandemic Threat Grows: H5N1 Spreads Globally, Human Risk Rises
Overview
H5N1 bird flu continues to spread widely among animals, raising concerns about pandemic potential. The WHO reports a high fatality rate in human cases, while scientists warn the virus's ability to jump species and mutate poses a significant threat. Simultaneously, a more virulent H3N2 strain is also emerging globally.
Pandemic Potential Looms
The highly pathogenic avian influenza (HPAI) H5N1 virus, first detected in 2020, is now in its sixth year of widespread geographical spread, impacting poultry, wild birds, and notably, cattle. Scientists warn that the current strain is infecting unprecedented numbers of animals globally.
The World Health Organization (WHO) reports that from January 1, 2003, to November 5, 2025, there have been 992 human infections with avian influenza A (H5N1) across 25 countries. Alarmingly, nearly 48% of these cases, totaling 476, were fatal.
Professor Ed Hutchinson of the University of Glasgow stated the virus is now a "global problem" and "completely out of control" as a disease of wild animals. "It's raging around the world, and there's no feasible containment method other than just watching it infect huge populations of animals," he noted.
Emerging Threats
The current H5N1 strain, a clade 2.3.4.4b, evolved between 2018 and 2020 and has spread worldwide. In the US alone, over 285 million birds have been affected since February 2022. Human transmission from poultry or cattle has resulted in 71 cases and two deaths in the US. While the virus has shown an ability to jump species, evidence for sustained human-to-human transmission remains absent, though studies suggest it is getting closer.
Research indicates the virus possesses increased virulence compared to previous variants. Experts fear that the increasing and widespread transmissions among species could facilitate the genome reassortment necessary to trigger a pandemic. Cambridge and Glasgow university research also suggests bird flu viruses are resistant to fever, potentially rendering human body temperature fluctuations ineffective as a defense mechanism, due to a gene allowing them to thrive at higher temperatures. In April 2025, the Global Virus Network urged improved surveillance and biosecurity measures globally.
A separate concern is the emergence of an Influenza A (H3N2) virus, which, while not related to bird flu, exhibits higher evolutionary traits, causing more severe epidemics. The US has reported a mix of A(H3N2) and A(H1N1) causing significant illness. Subclade K of H3N2 has been detected globally, partially evading immunity and accounting for 33% of all A(H3N2) cases worldwide by November 2025.
