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On the heels of a multi-state outbreak of highly pathogenic avian influenza A (H5N1) in dairy cows, experts told MedPage Today that a trio of H5N1 vaccines for humans has already been developed and approved in the U.S.

While there hasn't been an outbreak among people to put them to the test, human-to-human transmission would "drive the need" for H5N1 vaccines, Aaron Glatt, MD, of Mount Sinai South Nassau in Oceanside, New York and a fellow of the Infectious Diseases Society of America, told MedPage Today.

If infections among humans who work with animals become more common, this could be a subgroup of people to vaccinate, he added. So far, only one human case in the U.S. has been reported this year.

Nahid Bhadelia, MD, of the Boston University Center on Emerging Infectious Diseases, noted that it is "important to be talking about vaccines," including the current stockpile, the capacity to manufacture new doses if need be, and the designs of the current vaccines.

A spokesperson for the Administration for Strategic Preparedness and Response (ASPR) told MedPage Today in an emailed statement that it is , along with partners from the CDC, FDA, Department of Agriculture, and White House.

ASPR's National Pre-Pandemic Influenza Vaccine Stockpile (NPIVS) program "enables rapid response to influenza strains as they evolve," the spokesperson said, adding that the program "works closely with industry partners to make and test updated vaccines that match new strains of influenza viruses with pandemic potential as they emerge, while at the same time, supporting manufacturing capacity to allow for large-scale vaccine production if needed."

NPIVS is "continually generating antigens that are matched to virus strains of interest, and we have two antigens that are well-matched to the currently circulating strain of H5N1," the spokesperson added. "Hundreds of thousands of doses could be deployed within weeks pending regulatory action, and over 100 million doses could be deployed in the coming months."

Vaccine Makers Stand Ready

ASPR's industry partners include CSL Seqirus, GSK, and Sanofi, which have H5N1 vaccines licensed for use in the U.S.

Sanofi developed egg-based A/H5N1 vaccines as early as 2004 and received the first U.S. license for such a vaccine in 2007, a spokesperson for the company told MedPage Today.

"Our egg-based vaccine supply would well contribute to support a global influenza pandemic response should it arise either from A/H5N1 or any other influenza strain," the spokesperson said, adding that in December 2019, Sanofi entered into an agreement with the (BARDA) to "establish sustainable production of a recombinant vaccine for use in the event of a pandemic."

That would allow the company "to leverage the technology used for one of our approved seasonal flu vaccines to deliver a pandemic vaccine," the spokesperson said.

A spokesperson for GSK said the company is also monitoring the situation, along with the evolving epidemiology: "We are directly connected with our contractual partners to deliver on our commitments in the event that an influenza pandemic is declared."

However, "GSK is not planning to disrupt seasonal flu production plans while there is no global health emergency," the spokesperson added.

In 2022, the company was awarded multi-year contracts with the U.S., Canada, the European Union, and the WHO to supply its pandemic preparedness vaccine if the WHO declared an influenza pandemic, the spokesperson said. "These contracts will support the ready production and supply of this vaccine, and together could provide at least 200 million doses of pandemic influenza vaccine around the world."

As for what may be currently available for use, the spokesperson said that the company's pandemic vaccine is "developed to be updated with the latest circulating strains, and this follows the process for seasonal flu, where strains are identified by the WHO and vaccines are updated every season."

"The timeline for this depends on several factors, including the licensing processes, which would be determined when a pandemic is declared," the spokesperson noted.

For its part, CSL Seqirus said in a statement that it is able to "make a vaccine in response to government orders for use in a disease outbreak, for people who could be occupationally exposed to sick animals, or full-scale production of pandemic influenza vaccine should a pandemic be declared."

The company's manufacturing facility in Holly Springs, North Carolina, which was built through a public-private partnership with BARDA, "utilizes a highly scalable method of production and is positioned to deliver up to 150 million pandemic influenza vaccine doses to support a pandemic response if needed," the statement said, "in addition to its annual routine seasonal influenza vaccine production."

What Else Is Important?

At this point, stockpiling H5N1 vaccines for a specific clade is "just not practical," Glatt said.

However, if a different situation emerges, the time from when a vaccine may be needed to when a vaccine would be available would likely be shorter than historical cases, given the trio of already approved H5N1 vaccines and their safety data, he noted.

In the meantime, it is important to continue to recognize and address cases in poultry and other animal populations, Glatt added.

Bhadelia also expressed concern regarding the potential for more infections among animals and any significant spread among humans, which would increase the chances for evolution of the virus farther away from the current vaccines.

As for the ongoing development of vaccines, she pointed to potential interest in vaccines that are not egg-based, especially in the event of an outbreak affecting the egg supply, as well as vaccines that are not monovalent, such as universal influenza shots.

It is also crucial to think beyond vaccines alone, she added, especially when it comes to immunocompromised people and other more vulnerable individuals, including ensuring that an H5N1 vaccine strategy is backed up by the availability of antiviral treatments.

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