Researchers have recently identified a strain of influenza virus in pigs that has the potential to cause a global pandemic. This particular virus, known as H1N2, belongs to a lineage of flu viruses that originated in birds, adapted to pigs, and has now been detected in humans. Referred to as 1C H1N2, this strain exhibits characteristics that make it highly concerning in terms of pandemic risk.
Influenza A viruses are not limited to humans but also infect birds, pigs, horses, and other animals. In pigs, the main subtypes circulating are H1N1, H1N2, and H3N2, with genetic lineages based on their evolutionary history. The 1C lineage emerged in Europe in 1979 when an avian flu virus crossed into pigs, leading to the creation of a new strain. While this lineage has mainly been confined to swine populations in Europe and Asia, it has recently been detected in humans, raising alarms about potential transmission at the human-animal interface.
A recent study found that the 1C H1N2 virus has limited immunity among the population. Only about one-third of U.S. adults showed any detectable neutralizing antibodies, primarily from individuals born before 1950. This lack of immunity is attributed to residual immunity from the 1918-like viruses that circulated in the early 20th century, with more recent generations showing almost no immune recognition of the 1C H1N2 virus. Additionally, current seasonal flu vaccines offer minimal cross-protection against this strain.
Laboratory tests revealed that the 1C H1N2 virus possesses traits conducive to human-to-human transmission. It binds preferentially to receptors in the human upper respiratory tract, replicates efficiently in human airway cells, and remains stable in aerosol-like droplets across various humidity levels. Moreover, the virus demonstrated high neuraminidase activity, which is linked to increased transmissibility.
Transmission experiments using pigs and ferrets showed that the 1C H1N2 virus could successfully spread between species. Infected pigs housed near uninfected ferrets resulted in all ferrets developing antibodies against the virus, indicating transmission. Even ferrets with prior immunity to the 2009 H1N1 pandemic strain became infected, highlighting the virus’s ability to overcome existing immunity barriers.
The pandemic risk assessment framework categorizes viruses based on specific traits, with the 1C H1N2 virus meeting many of the criteria for high-risk potential. While the severity of a potential pandemic caused by this virus remains uncertain, early detection and risk assessment are crucial given its high transmissibility in humans.
In conclusion, the emergence of the 1C H1N2 virus emphasizes the importance of structured risk assessment and detailed experimental investigation. Researchers have combined serology, molecular virology, and animal models to evaluate this virus, providing valuable insights into a potential threat that might otherwise go unnoticed. While the severity of a pandemic caused by this virus is unknown, this study serves as a vital foundation for monitoring and addressing this high-risk flu virus.
