Scientists around the world are making steady progress toward developing a “universal” flu vaccine that could provide broader and longer-lasting protection than current seasonal shots, reports BBC.
Influenza infects roughly a billion people each year and causes between 290,000 and 650,000 deaths globally. Because the virus constantly evolves, flu vaccines must be updated annually — and their effectiveness can vary widely.
“The flu virus is a constantly moving target,” said Julie Ostrowsky of the Center for Infectious Disease Research and Policy at the University of Minnesota. Seasonal vaccines typically offer up to 60% protection in good years, but their performance drops when circulating strains differ from predictions.
Each year, the World Health Organization convenes experts to analyse global influenza data and recommend strains for vaccines in the Northern and Southern Hemispheres. However, unexpected variants can still emerge after recommendations are made, complicating protection efforts.
"That's why you have to get a flu shot every year," says Nicholas Heaton, a professor at the Duke University School of Medicine in North Carolina, US. Seasonal flu vaccines prevent many deaths and serious illnesses each year, but they are imperfect. Their effectiveness typically tops out around 60% and can dip well below that in years when the vaccine's formula isn't a good match for the virus that is actually spreading among humans.
But what if you didn't have to get a new shot every year? Heaton's lab, and others around the world, are trying to answer that tantalising question. They're developing so-called "universal" flu vaccines, which aim to offer better, broader and more durable protection than current seasonal vaccines. The idea is to "cover more strains or make the shot last longer", Heaton says. "Or, hopefully, both."
There are currently about a dozen such vaccine candidates moving through the clinical trial process and many others still in earlier stages of development, according to an initiative that tracks next-generation influenza vaccine development.
It's a "pretty amazing collection of projects", says Julie Ostrowsky, a research scientist at the University of Minnesota's Center for Infectious Disease Research and Policy, in the US, who works on the tracking project. But it is a complex challenge, she says. "It's not going to happen overnight."
Here's how scientists are taking a stab at the problem.
The term "the flu" is a bit misleading. Influenza is not a single entity, but many different viruses circulating between people and animals. And these viruses are constantly evolving, allowing them to stay one step ahead of human immune systems. "Flu varies a lot," Ostrowsky says. "It's just a constantly moving target."
A mutation here or there may not be enough to outsmart the immune system. But over time, the changes accumulate enough that the body's immune defences are rendered out of date, forcing them to play catch-up. That's why it's so difficult to formulate the flu shot each year. Public health officials and vaccine makers are, in effect, trying to predict the future, making their best guesses about how the virus will change and which specific strains will circulate in the season ahead.
To do so, the World Health Organization (WHO) convenes an international group of experts to pore over reams of data on where influenza is spreading and how it's evolving. Last time they printed all this data, they racked up a 10cm thick stack of double-sided papers, says Wenqing Zhang, from the WHO's department of Epidemic and Pandemic Threats Management.
Each February, the WHO's expert group meets to create recommendations for shots used in the Northern Hemisphere, where flu season typically starts around October. In September, they do the same for the Southern Hemisphere, where flu season typically starts around April.
But a lot can change after these predictions are made. In the 2025-2026 season, for instance, flu outbreaks have been occurring around the world caused by H3N2 subclade K influenza viruses, which weren't even on the WHO's radar in February 2025. "At that time, there was no clade K virus yet," Zhang says, so there wasn't a recommendation to tailor vaccines accordingly.
Despite the surprise, preliminary data out of the UK suggest this year's shots are nonetheless protecting against severe illness and hospitalisation for subclade K, and they seem to work particularly well among children. But the sudden arrival of subclade K shows that influenza can "give us a surprise at a time", often when we don't anticipate it, Zhang says.
Bd-pratidin English/TR
