The highly pathogenic avian influenza (HPAI) strain H5N1, which caused widespread concern and claimed numerous lives between 2003 and 2023, seemed to have lost its deadly edge. The virus, primarily transmitted through close contact with infected birds, resulted in a mortality rate of over 50% among diagnosed cases during its peak.
In recent years, there has been a significant decrease in human cases and fatalities associated with avian H5N1. This decline brought a sense of relief to individuals with potential exposure, as experts believed that the strains of H5N1 circulating in poultry markets had lost their potency and were no longer a major concern for human health.
This positive development offered a glimmer of hope in the fight against avian influenza. Not only did the virus no longer cause widespread deaths, but it also appeared to lack the ability to spread through airborne transmission among mammals, a primary route for influenza contagion. Nevertheless, experts had long warned about the potential for an H5N1 pandemic. In a 2012 study, researchers identified that two out of five necessary genetic changes required for the virus to become transmissible among ferrets were already prevalent in nature. The addition of just a few more mutations could potentially transform H5N1 into a pandemic risk capable of human-to-human transmission.
Recent observations have highlighted the reemergence of avian H5N1 and its expanding reach. A study published in The Lancet Infectious Diseases revealed that in 2021, the virus established a year-round presence in wild birds in Europe, subsequently spreading to North and South America. The persistent circulation of H5N1 among wild bird populations has led to the deaths of millions of poultry birds in the United States and Europe.
Concerns have grown as repeated outbreaks among mammals could provide opportunities for the virus to mutate and pose an increased threat to humans. Indeed, H5N1 has already infected around 30 mammalian species, leading to outbreaks and fatalities in North American seals and farmed minks in Spain. Scientists suspect that these animals may be spreading the virus through droplets or aerosols during close-range interactions.
While efficient human-to-human transmission of H5N1 is not currently observed, the evolving nature of the virus raises concerns. The World Health Organization (WHO) reported a decline in human H5N1 cases to zero by 2018. However, there has been a recent uptick in reported cases, albeit at low numbers. Cambodia, for example, recorded one death from H5N1 this year. The Lancet study authors underscored the global spread of highly pathogenic avian influenza as a cause for concern, given its impact on wild birds, poultry, and the rising number of reported cases in mammals, including humans.
Mitigating the risk of an H5N1 pandemic and minimizing its potential consequences require proactive measures. The Lancet authors advocate for enhanced disease surveillance in pig, poultry, and mink operations, as well as reducing the size of poultry farms, implementing chicken vaccination programs, and strengthening biosecurity regulations. Drawing from successful experiences in the past, such as the 2013 H7N9 avian influenza outbreak in China, where an aggressive poultry vaccination campaign led to a significant drop in human cases, vaccination strategies for H5N1 hold promise.
While there is currently no urgent concern about H5N1 posing a direct threat to humans, its high case fatality rate remains a cause for vigilance. Efforts should be made to develop effective vaccines promptly. If pharmaceutical companies are hesitant to invest in early vaccine development due to financial risks, governments should step in and provide necessary funding to ensure preparedness for any potential H5N1 pandemic.
Source: TheBulletin