The outbreak of bird flu in US dairy cows is leading to the development of new next-generation mRNA vaccines – similar to COVID-19 vaccines – that are being tested in both animals and humans.
Next month, the U.S. Department of Agriculture will begin testing a vaccine developed by researchers at the University of Pennsylvania by giving it to calves. The idea: If vaccinating cows protects dairy workers, it could mean the virus is less likely to jump to humans and mutate in ways that could fuel human-to-human spread.
In the meantime. The U.S. Department of Health and Human Services has been talking to manufacturers about possible mRNA flu vaccines for humans that could, if necessary, supplement the millions of doses of bird flu vaccines already in government hands.
“If a pandemic breaks out, there will be a huge demand for vaccines,” said Richard Webby, a flu researcher at St. Jude Children’s Research Hospital in Memphis. “The more different platforms (vaccine production) can respond to that, the better.”
The bird flu virus has been spreading among more and more animal species in many countries since 2020. It was discovered in US dairy herds in March, although researchers believe it may have been occurring in cows since December. This week, the USDA announced that it had been found in alpacas for the first time.
At least three people – all workers on farms with infected cows – have been diagnosed with bird flu, although the illnesses were considered mild.
But earlier versions of the same H5N1 flu virus are very deadly to people in other parts of the world. Officials are taking steps to be prepared if the virus mutates in a way that makes it deadlier or spreads more easily from person to person.
Traditionally, most flu vaccines are made through an egg-based manufacturing process that has been used for more than 70 years. It involves injecting a candidate virus into fertilized chicken eggs, which are incubated for several days to allow the viruses to grow. Fluid is harvested from the eggs and used as a basis for vaccines, where the killed or weakened virus stimulates the body’s immune system.
Instead of eggs – also vulnerable to supply constraints caused by bird flu – a flu vaccine is made in giant vats of cells.
Officials say they already have two vaccine candidates for humans that appear to be a good match for the bird flu virus in U.S. dairy herds. The Centers for Disease Control and Prevention used the circulating bird flu virus as the seed for them.
The government has hundreds of thousands of vaccine doses in pre-filled syringes and vials that could likely go out within weeks if needed, federal health officials say.
They also say they have bulk antigen that could generate nearly 10 million additional doses that could be filled, finished and distributed within a few months. CSL Seqirus, which produces cell-based flu vaccines, announced this week that the government has hired it to fill and finish about 4.8 million of those doses. The work could be done by the end of the summer, U.S. health officials said this week.
But flu vaccine production lines are already busy with this fall’s seasonal shots — work that would have to be paused to produce millions more doses of bird flu vaccine. That’s why the government has taken a different, faster approach: the mRNA technology used to produce the primary vaccines against COVID-19.
These messenger RNA vaccines are made using a small piece of genetic material from the virus. The genetic blueprint is designed to teach the body how to make a protein used to build immunity.
The pharmaceutical company Moderna already has an mRNA vaccine for bird flu that is being tested on humans at a very early stage. In a statement, Moderna confirmed that “we are in discussions with the US government about advancing our pandemic flu candidate.”
Similar work is taking place at Pfizer. Company researchers in December gave human volunteers an mRNA vaccine against a strain of bird flu that is similar to — but not exactly the same as — that found in cows. Since then, researchers have conducted a laboratory experiment in which blood samples from these volunteers were exposed to the strain found on dairy farms and saw a “remarkable increase in antibody responses,” Pfizer said in a statement.
As for the cow vaccine, Penn immunologist Scott Hensley worked with mRNA pioneer and Nobel laureate Drew Weissman to produce the experimental doses. Hensley said the vaccine is similar to the Moderna vaccine for humans.
In initial tests, mice and ferrets produced high levels of antibodies against the bird flu virus after vaccination.
In another experiment, researchers vaccinated and deliberately infected a group of ferrets, then compared what happened to ferrets that had not been vaccinated. All the vaccinated animals survived and the unvaccinated ones did not, Hensley said.
“The vaccine was really successful,” says Webby, whose lab did that work last year in collaboration with Hensley.
The study in cows will be similar to the first-step tests initially conducted in smaller animals. The plan is for about ten calves to be vaccinated initially, half with one dose and the other half with another. Their blood is then taken and examined to determine how many antibodies against bird flu have been produced.
The USDA study will first need to determine the appropriate dose for such a large animal, Hensley said, before testing whether it protects them like smaller animals.
What scares me most is the amount of interaction between livestock and people, Hensley said.
“We’re not talking about an animal that lives on a mountaintop,” he said. “If this was a bobcat outbreak, I would feel sorry for the bobcats, but that’s not a major human risk.”
If a vaccine reduces the amount of virus in the cow, “we ultimately reduce the chance of a mutant virus emerging and spreading among people,” he said.
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