Avian Flu: US Cattle and Dairy Stocks Under Strict Scrutiny, Vaccine Becomes Concern

PETALUMA, CALIFORNIA - APRIL 26: Cows graze in a field at a dairy farm on April 26, 2024 in Petaluma, California. The U.S. Department of Agriculture is ordering dairy producers to test cows that produce milk for infections from highly pathogenic avian influenza (HPAI H5N1) before the animals are transported to a different state following the discovery of the virus in samples of pasteurized milk taken by the Food and Drug Administration. (Photo by Justin Sullivan/Getty Images)

United States: The prevalence of avian flu within American cows and dairy stocks has stirred vigilance among vaccine researchers.

Historically, avian influenza has left its mark on humans. In the tumultuous throes of 1918, a strain ravaged war-weary populations, claiming the lives of over 50 million individuals – a toll unrivaled by any other documented disease outbreak. Presently, a highly virulent variant of avian flu, denoted as H5N1, precipitates a global animal epidemic, albeit human affliction with this strain remains exceedingly rare.

Since its emergence in 1996, this strain has precipitated the demise of billions of poultry fowl, decimated millions of avian species in the wild, and infected no less than 48 varieties of mammals. Within the United States, barnyard felines have succumbed to consuming the unpasteurized milk of H5N1-infected cattle, as per the reports by BBC News. 

This most recent iteration has yet to acclimatize to facile human-to-human transmission. Since 2003, 463 fatalities have been attributed to this virus, which boasts a daunting mortality rate of over 50% among humans. Hitherto, instances of human-to-human transmission have purportedly been sporadic and short-lived.

Nonetheless, the potential for interspecies transmission may be evolving.

In the month of March, the variant was observed proliferating among bovine populations in tandem with avian hosts. By April, a ranch hand in Texas became the inaugural individual to contract the virus from a bovine source. With contemporary bovine husbandry presenting a fertile breeding ground for the virus, the likelihood of further mutations conducive to enhanced mammalian transmission, including humans, looms large, caution scientists.

Should the virus acquire the capacity for efficient human transmission, a vaccine could serve as a means to impede its advance. As per the pronouncement of the World Health Organization (WHO), the virus has yet to reach a juncture necessitating a human vaccine. Nevertheless, in anticipation of such an eventuality, the organization affirms the presence of frameworks and strategies poised to facilitate vaccine production, the reports by BBC unveiled.

BBC Future Planet engaged in dialogue with Maria Van Kerkhove, an epidemiologist and interim overseer of epidemic and pandemic readiness and prevention at WHO, regarding the prospective trajectory of producing and deploying a human vaccine against avian flu.

Has the infiltration of avian influenza into American bovine populations, along with its identification in dairy products, intensified the urgency for a human vaccine?

The incursion of novel hosts invariably reshapes our comprehension of the virus: with each successive cycle of transmission, the virus accrues opportunities for mutation and human infection.

Presently, we observe inter-farm dissemination among bovine populations in the US, with myriad ongoing investigations endeavoring to elucidate the patterns of virus circulation among these agrarian enclaves. Regarding the presence of H5N1 in milk, collaborative efforts are underway, with numerous researchers probing the efficacy of pasteurization and viral inactivation. Thus, it remains imperative for consumers to exclusively patronize pasteurized dairy products.

However, human vaccines cater to humans. As of the time of this interview, we have only recorded 28 documented human cases since 2021, with no instances of documented human-to-human transmission. For WHO to advocate heightened development or production of H5N1 vaccines, a significant alteration in the risk profile for humans would need to manifest.

At what juncture would the implementation of a human vaccine against avian flu become imperative?

To assess transmissibility and severity, particularly in the event of heightened human-to-human transmission, WHO routinely conducts risk evaluations based on extant data. In addition to the virus’s genetic composition, such assessments encompass the phenotypic attributes of the virus – its modus operandi in the natural realm. Would transmission be confined to individuals in close proximity, such as healthcare workers? Would it precipitate isolated clusters of infection? Or widespread transmission with large-scale outbreaks?

What mechanisms are in place to orchestrate a rollout?

In contradistinction to the advent of Covid-19, stemming from the Sars-CoV-2 virus, our apparatus for studying influenza viruses spans seven decades.

Termed the Global Influenza Surveillance and Response System (GISRS), this international coalition comprises 150 national influenza centers across 130 member states – encompassing 12 facilities dedicated to H5 strains. These centers are currently monitoring the circulation of influenza viruses to identify potential epidemic and pandemic subtypes.

Additionally, we possess the Pandemic Influenza Preparedness framework (PIP), which, in tandem with GISRS, identifies candidate vaccine strains, facilitating expedited vaccine production. Under this framework, several H5N1 vaccines are already in the pipeline.

Scaling up vaccine development and manufacturing necessitates a proclamation by WHO – predicated on the aforementioned risk assessments – indicating a virus with pandemic potential. Upon such declaration, extant agreements empower the transition from seasonal influenza vaccine production to pandemic vaccine manufacture.

However, we have yet to reach that juncture. Human-to-human transmission remains elusive.

Are vaccine manufacturers equipped to address a potential mutation of avian influenza, facilitating efficient human transmission?

In the wake of a novel pathogen, global susceptibility to infection is universal, as evidenced by the emergence of Sars-CoV-2.

The susceptibility of the populace to H5N1 remains undetermined. Surveys on H5N1 prevalence have been conducted to gauge population exposure, with only individuals directly engaged with poultry – such as occupational exposure – manifesting illness thus far.

With respect to this virus, global surveillance mechanisms are in place. Moreover, a repository of “candidate vaccine viruses” stands at the ready, affording manufacturers the resources to develop vaccines. Among these, two candidate vaccine viruses pertinent to the circulating H5N1 strain are readily accessible, positioning us favorably for accelerated production if necessitated.

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