After a promising experiment, a single-dose vaccine has been developed that could stop the next pandemic

A vaccine that protects against all forms of influenza could be available within five years, a team of scientists has announced, after a "promising" trial on animals.

The flu virus is constantly mutating, so new vaccines are needed every year to prevent infection. But scientists in the United States said their "innovative" approach targets a part of the virus that does not mutate.

An early trial in monkeys showed that the vaccine technology, designed based on a 100-year-old virus, generated a “robust immune response” against a modern variant.

The scientists said their work raises hope that a "single, effective" vaccine could emerge that provides lifelong immunity against the mutated virus.

"It's exciting because in most cases, this kind of basic science research advances science incrementally," said Jonah Sacha, a professor at Oregon Health & Science University in the US. "This could actually become a vaccine in five years or less."

Current flu vaccines target proteins that protrude from the surface of the virus, known as spike proteins.

But the spike proteins can mutate to evade antibodies, which the body's immune system produces to defend against the virus.

In the study, published in the journal Nature Communications, the scientists used a vaccine technology originally developed to combat HIV. It works by using a harmless herpes virus, called cytomegalovirus (CMV), to deliver a piece of genetic code from the flu virus into cells in the body to mimic an infection.

The vaccine platform is designed to target the core of the virus, which unlike spike proteins, does not mutate over time, the scientists said.

The team tested the vaccine on 11 monkeys infected with H5N1, a bird flu virus that experts believe has the potential to become the next human pandemic.

But this technology was based on a deadly virus dating back a century that killed an estimated 50 million people worldwide.

Six monkeys vaccinated against the 1918 Spanish flu survived exposure to the more modern H5N1 virus, the team said.

In contrast, unvaccinated monkeys in the control group that were exposed to H5N1 died from the disease, they added.

The scientists noted that their approach targets a specific type of immune cell in the lungs known as effector memory T cells, which are able to recognize proteins at the heart of the virus that do not mutate.

“It worked because the virus’s internal protein was so well preserved,” said Professor Sacha. “Even after nearly 100 years of mutation, the virus cannot change these very important parts of itself.”

The team explained that this study raises the possibility of developing a vaccine against the H5N1 virus in humans.

“If a deadly virus like H5N1 infects humans and causes a pandemic, we need to quickly validate and deploy a new vaccine,” said Douglas Reed, associate professor of immunology at the University of Pittsburgh’s Vaccine Research Center in the United States.

The scientists added that their vaccine technology, licensed from immunology company Vir Biotechnology, could also work on other viruses, such as Sars-CoV-2, which causes Covid-19, to provide long-term immunity.