US-funded scientists said Thursday they have devised an experimental vaccine against a common childhood illness called respiratory syncytial virus (RSV).

There is currently no vaccine on the market for RSV, which is the world's second-leading killer of babies aged one month to one year, after malaria.

RSV causes inflammation in the small airways of the lungs and is the most common cause of pneumonia in babies and of hospitalization of children under five.

“Many common diseases of childhood are now vaccine-preventable, but a vaccine against RSV infection has eluded us for decades,” said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

“This work marks a major step forward," he said, citing promising animal studies that showed a wide-ranging protective effect.

Planning is under way for human trials of the vaccine.

The research on the vaccine and its structure-based design is described in the journal Science.