US scientists say they have developed an experimental nasal spray that could offer broad protection against a wide range of respiratory illnesses – including coughs, colds, flu and even some bacterial lung infections. The early-stage work, led by Stanford University, has so far only been tested in animals, with human trials still needed.

Unlike traditional vaccines, which train the body to recognise one specific virus or bacterium, this approach works in a completely different way. Rather than targeting a single pathogen, the spray appears to keep key immune cells in the lungs on standby, ready to react quickly to whatever tries to enter.

In animal experiments, the researchers found the effect lasted for roughly three months. During that time, viruses were reduced by between 100 and 1,000 times in the lungs. The team also reported protection against two bacterial species, including Staphylococcus aureus and Acinetobacter baumannii. They even saw signs the immune response to house dust mite allergens was dampened, which could be relevant for allergic asthma.

Experts have described the findings as promising but warned there are major unknowns. It is unclear whether the same results will translate to people, how long any protection might last, and whether keeping the immune system “on alert” could trigger unwanted inflammation. The researchers believe the spray could complement existing vaccines, particularly during winter or the early stages of a new pandemic.