Avian Flu Vaccine Relies on Eggs, Sparking Concern Among Scientists

FILE PHOTO: Test tubes labelled "Bird Flu" and eggs are seen in this picture illustration, January 14, 2023. REUTERS/Dado Ruvic/Illustration/File Photo

United States: Even the mere mention of a nascent flu pandemic sends scientists into a flurry about the fragility of egg-based vaccine production. This concern was evident in 2005, surfaced again in 2009, and persists today, as millions of fertilized hen eggs remain the cornerstone of vaccine production intended to shield the populace from novel influenza strains.

“It’s almost ludicrous to rely on a technology from the 1940s to combat a 21st-century pandemic,” remarked Rick Bright, former head of the Health and Human Services Department’s Biomedical Advanced Research and Development Authority during the Trump era.

The humor fades quickly, he noted, when considering that the current H5N1 bird flu vaccine formulation demands two doses, each containing an extensive 90 micrograms of antigen, yet delivers only moderate immunity. “To meet the US needs alone, we would require hens to lay 900,000 eggs daily for nine months,” Bright elaborated, as highlighted by CBS News.

This scenario assumes the chickens remain uninfected.

The proliferation of avian flu has ravaged bird populations, causing fatalities among barn cats and other mammals, with livestock in no fewer than nine states and at least two individuals in the US having contracted the virus, prompting renewed vigilance over the threat of a global pandemic.

Presently, the sole confirmed human cases in the US involved dairy workers in Texas and Michigan who developed conjunctivitis and recovered swiftly. Nonetheless, the virus’s extensive spread across species and territories heightens the risk of mutations, leading to a strain capable of airborne human-to-human transmission, resulting in respiratory illnesses.

Should such a mutation occur, the vaccine genesis starts with the egg.

To cultivate the viral material for an influenza vaccine, millions of fertilized eggs are employed. Challenges arise when the virus doesn’t proliferate efficiently or mutates such that the resultant vaccine induces antibodies ineffective against the wild virus, which may also evolve beyond the vaccine’s protection. A dire prospect remains that wild birds could introduce the virus into henhouses essential for vaccine production.

“Once those chickens are infected, vaccine production ceases,” Bright warned.

Post-2009, when the H1N1 swine flu pandemic unfolded globally before vaccines were widely available, researchers and governments have sought alternatives. Billions have been allocated to develop vaccines using mammalian and insect cell lines, mitigating the risks associated with egg-based production, as per CBS News.

“Cell-based vaccines are universally acknowledged as superior—more immunogenic and easier to produce,” stated Amesh Adalja, an infectious disease expert at Johns Hopkins University’s Center for Health Security. “Yet, the dominance of egg-based manufacturing stymies their progress.”

Manufacturers of cell-based influenza vaccines, such as CSL Seqirus and Sanofi, also have substantial investments in egg-based production infrastructure that they are reluctant to abandon. “Vaccine companies responding to outbreaks like Ebola, Zika, or COVID often face financial losses,” explained Nicole Lurie, former HHS assistant secretary for preparedness and response and current executive director of CEPI, the global epidemic-prevention organization.

Notable exceptions include the mRNA vaccines developed for COVID-19, although even Pfizer and Moderna have disposed of millions of surplus doses as demand diminished.

Both Pfizer and Moderna are trialing mRNA-based seasonal influenza vaccines, and the government is inviting bids for mRNA pandemic flu vaccines, according to David Boucher, director of infectious disease preparednesss at HHS’ Administration for Strategic Preparedness and Response.

Bright, who facilitated a billion-dollar investment in a cell-based flu vaccine facility in Holly Springs, North Carolina, asserted, “We cannot combat an H5N1 pandemic with an egg-based vaccine.” For the time being, however, options remain limited.

BARDA has accumulated hundreds of thousands of doses of an H5N1 vaccine that elicits antibodies neutralizing the currently circulating virus. Boucher indicated that millions more doses could be produced within weeks and up to 100 million doses in five months.

Nevertheless, the vaccines in the national stockpile don’t perfectly match the current virus strain. Even with two doses containing six times the antigen of standard flu vaccines, their efficacy against the circulating strains was partial, Adalja noted.

BARDA is funding clinical trials for a vaccine candidate that “matches the virus found in cattle,” Boucher said, CBS News highlighted.

While flu vaccine manufacturers are gearing up for this fall’s inoculations, the federal government might eventually pivot production to focus on a pandemic-specific strain.

“We lack the capacity to produce both simultaneously,” Adalja pointed out.

Currently, ASPR maintains a stockpile of bulk pandemic vaccine and has designated sites where 4.8 million doses could be bottled and finalized without halting seasonal flu vaccine production, ASPR chief Dawn O’Connell stated on May 22.

Efforts to diversify away from egg-based vaccines began in 2005 with the avian flu scare and intensified post-2009. “With our current resources, leveraging the existing seasonal infrastructure, which remains predominantly egg-based, provides the best value to taxpayers,” Boucher explained.

Flu vaccine producers “have an effective system for seasonal vaccine production,” he added. Without significant financial incentives, “we’re likely to rely on eggs for the foreseeable future.”

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