Influenza is highly mutable virus, with scientists constantly playing catch up by twice a year releasing new formulations targeting the latest viral strains. In a move that could lead a universal flu vaccine, researchers have identified a type of influenza-fighting white blood cell found in nasal tissue that could pave the way for the development of a "one-shot" vaccine that is effective against all strains.

Most previous research into a universal flu vaccine focused on a specific white blood cell, called resident memory CD8 T cells, or Trms. These Trms cells have been shown to be excellent in targeting a variety of influenza strains, meaning if a vaccine that induced these cells could be developed, then a single treatment would remain effective for many years.

"Our current flu vaccines work by training the body to recognize a component on the surface on an influenza virus particle," says Dr Linda Wakim from the University of Melbourne. "Instead of recognizing external parts of the virus, which are constantly changing, these cells are trained to recognize internal parts of the virus."

The big challenge researchers faced in working with these Trms cells has been the cells' incredibly short lifespan. Previous studies looking at Trms cells in the lungs showed they tended to diminish at a fast rate, meaning that within 100 days of a treatment they would mostly have disappeared.

In a new study, a group of researchers at the University of Melbourne found a previously undiscovered source of Trms cells living in nasal tissue and, most strikingly, these cells could live for a very long time. As well as finding these long-lasting Trms cells, by shifting their focus from the lungs to the nose the researchers hope to develop a vaccine that can stop the virus at the point of inhalation, rather than letting it gain a foothold in the upper airways and migrate to the lungs.

"We took a step back and thought, 'What if we could stop the virus in the nose before it made it to the lung?'" says Dr Wakim. "We moved our focus to investigating immune responses in nasal tissue, which is where the body first encounters flu viruses – a kind of nasal border patrol."

Fighting influenza at the site of infection with these long-lasting Trms cells could be the key to developing a new, one-shot, flu vaccine. The researchers are now working on a way to induce production of these nasal Trms cells and lodge them into the nasal tissue.

The study was recently published in the journal Science Immunology.