Sri Lanka, Feb. 24 -- Scientists at Stanford University say they are developing a single nasal spray vaccine that could protect against coughs, colds, flu, and even dangerous bacterial lung infections. Early research in animals suggests the spray may also reduce allergic reactions, including asthma triggered by dust mites.

The research, published in the journal Science, marks a dramatic shift in how vaccines work. Instead of training the immune system to fight one specific virus, the new approach boosts the body's frontline defenses in the lungs. Experts say the findings are exciting but stress that human clinical trials are still needed.

For more than 200 years, vaccines have followed the same principle. They train the immune system to...