Clinical Trials Of 'Universal' Flu Vaccine That Blocks Multiple Strains Show Promise

While the current COVID-19 pandemic has rightly taken precedence in our public health concerns at the moment, seasonal influenza continues to be linked to hundreds of thousands of deaths worldwide every year. Now, scientists think they may be one step closer to formulating a universal flu vaccine.

Such a vaccine would offer long-lasting protection against a wide variety of flu strains, which can mutate and evolve to escape the reach of the flu vaccines we have today. Having a vaccine like this would make a huge difference to public health, and many research teams are looking for one.

This new solution has just completed the first stage of human clinical trials, designed to evaluate its safety. It passed with flying colours, and though the sample size was small – just 65 people – it's a promising start to what will hopefully be a long-term life saver.

"An influenza virus vaccine that results in broad immunity would likely protect against any emerging influenza virus subtype or strain and would significantly enhance our pandemic preparedness, avoiding future problems with influenza pandemics as we see them now with COVID-19," says microbiologist Florian Krammer, from the Icahn School of Medicine at Mount Sinai, New York City.

"Our chimeric hemagglutinin vaccine is a major advance over conventional vaccines which are often mismatched to the circulating strains of virus, impacting their effectiveness. In addition, revaccinating individuals annually is a huge and expensive undertaking."

Just two or three shots of the chimeric hemagglutinin (HA)-based vaccine would be enough to push the body's immune system into developing immunity, the researchers say, and it wouldn't have to be reformulated each year.

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The vaccine is so named because it targets the hemagglutinin protein that binds the influenza virus to host cell receptors in the body. Influenza vaccines usually encourage the body to produce antibodies that target the globular head domain, or tip, of the protein. In this case, though, researchers took aim at the stalk domain further down, closer to the virus's shell.

While the flu virus is typically able to use a process called antigenic drift to counter neutralisation by mutating the head of the hemagglutinin protein, that escape route isn't available through the stalk part. It's a fixed target rather than a changing one.

"The beauty of this vaccine is that it's not only broad, but multifunctional with stalk-specific antibodies that can neutralise many kinds of influenza viruses," says microbiologist Adolfo García-Sastre, from the Icahn School of Medicine.

"This universal vaccine could be particularly beneficial to low and middle-income countries that don't have the resources or the logistics to vaccinate their populations each year against influenza."

The participants that received the jab developed strong immune responses that lasted at least 18 months, which is promising. As this is just a Phase 1 trial though, the volunteers weren't directly tested for protection against influenza – that first stage just deals with safety.

Although scientists have long thought that the stalk section of hemagglutinin might be key to developing a universal vaccine, it hasn't been clear if this part of the protein could actually be properly targeted. The new study suggests so.

Over the next couple of years, the researchers will be busy developing similar vaccines to target other influenza groups, before combining them together and organising a larger scale human trial to test immunity directly. After that, we might start seeing flu seasons that aren't quite so deadly.

"This phase of our clinical work significantly advances our understanding of the immune response in terms of its longevity, and leaves us greatly encouraged about future progress for this potentially breakthrough vaccine," says Krammer.

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