One step closer to a universal flu vaccine?

One step closer to a universal flu vaccine?

Imagine a single dose of vaccine that prepares your body to fight off all known strains of flu – a so-called universal flu vaccine that scientists have been trying to create for decades.

A new study describes successful animal trials of such a vaccine, offering hope that the country can be protected against future flu pandemics. Like the Covid vaccines made by Pfizer-BioNTech and Moderna, the experimental flu vaccine relies on mRNA.

It’s in its early stages – only tested in mice and ferrets – but the vaccine provides important evidence that a single shot could be used against an entire family of viruses. If the vaccine is successful in humans, the approach could be used against other virus families, possibly including the coronavirus.

The vaccine would not replace annual flu shots, but would provide a shield against serious illness and death from potential pandemic threats.

“There is a real need for new flu vaccines to provide protection against the pandemic threats that exist,” said Scott Hensley, an immunologist at the University of Pennsylvania who led the work.

“If there is a new flu pandemic tomorrow, if we had a vaccine like this that was widely used before this pandemic, we might not have to stop everything,” he said. He and his colleagues described the vaccine last week in the journal Science.

By age 5, most children have been infected with the flu several times and have acquired some immunity, but only to the strains they have encountered.

“Our childhood flu exposures create a long-lasting immune memory that can be recalled later in life,” Dr. Hensley said. But “we kind of live the rest of our lives based on the chance of everything that infected us when we were kids.”

Current flu vaccines protect against seasonal flu, but would offer little protection against a new strain that could become a pandemic threat. During the 2009 H1N1 swine flu pandemic, for example, the conventional vaccine offered little defense against the virus. But older people who had been exposed to H1N1 strains in childhood developed only mild symptoms.

Scientists have long tried to create a vaccine that would introduce children to every possible strain of flu they might encounter later in life. But the researchers were limited by technical obstacles and by the diversity of the influenza virus.

Broadly speaking, there are 20 flu subgroups that each represent thousands of viruses. Current vaccines can target a maximum of four subgroups. But the experimental vaccine contains all 20, and it would be faster to produce.

The vaccine elicited high levels of antibodies against all 20 flu subtypes in ferrets and mice, the researchers found – a finding that several experts called unexpected and promising.

If the vaccine behaves the same way in humans, “we will have broader coverage of influenza viruses – not just those that are circulating, but those that could spill over from the animal reservoir and cause the next pandemic,” Alyson Kelvin, a vaccinologist at the University of Saskatchewan in Canada, said.

Packing 20 targets into a single vaccine has a downside: antibody levels in the animals tested were lower than those given to them with vaccines for individual strains. But the levels were still high enough to be effective against the flu.

Because a new pandemic flu strain might differ from the 20 targets included in the experimental vaccine, the researchers also tested it against viruses that were not perfectly matched. The vaccine still offered strong protection, suggesting it would prevent at least serious illness, if not infection, from a new pandemic flu virus.

This phenomenon is similar to that of current Covid vaccines: although the latest variants of Omicron are so different from the ancestral virus that the original vaccine does not prevent infections, it continues to help protect most people against serious diseases. .

This quality may be a particular advantage of mRNA vaccines, Dr. Kelvin said. Conventional flu vaccines only target the specific viruses for which they are designed. But mRNA vaccines appear to produce antibodies that defend the body against a wider range of viruses than those included.

Experts noted some important caveats and questions that need to be answered before the vaccine becomes a viable candidate.

The animals in the study built equal defenses against all 20 flu strains. But “these animals have never seen influenza before,” said Richard J. Webby, an influenza virus expert at St. Jude Children’s Research Hospital in Memphis.

Such a complete lack of flu immunity is only true for very young children, Dr. Webby noted. Older people are exposed to many different strains over their lifetime, and it’s unclear whether their immune responses to a universal vaccine would be so uniform.

“The proof of the pudding will be what happens when it gets into humans and how getting into a pre-immune population will skew the response,” Dr Webby said.

Designing universal vaccines for different age groups, if needed, would be a challenge. It would also be important to see how long the protection of such a vaccine lasts, some experts said.

“The biggest issue with universal flu is what you should target and how long you can keep using the same vaccine,” said Ted Ross, director of global vaccine development at the Cleveland Clinic. “If you have to keep updating it, it may not increase the benefit of how we make vaccines today.”

The next step for the vaccine would be to test it on monkeys and on humans. But proving its effectiveness could be difficult. “How do you assess and regulate a vaccine whose targets aren’t circulating and therefore you can’t really show efficacy?” said Dr. Kelvin.

Perhaps the vaccine could be tested in small, sporadic outbreaks, or in poultry workers who are at risk of being infected with an avian flu virus, she said: “These are questions I think we need to respond before we have our next pandemic.

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