A common virus that causes wheezing and pneumonia claims the lives of up to two hundred thousand children worldwide each year, a study has found.
The research, conducted by the University of Edinburgh, also showed that about 3.4 million children require hospital treatment for severe lung infection caused by the bug - respiratory syncytial virus (RSV).
RSV - which infects most children before the age of two - usually causes mild cold-like symptoms, but can lead to serious illness in babies who are born prematurely or who have congenital heart disease.
The study, published in the Lancet journal, confirms that RSV is the single largest cause of lung infection in children. It is the first time that the numbers of children dying globally from RSV before the age of five has been quantified.
The international team analysed unpublished data from developing countries as well as all the published medical research on RSV infection. They found that about 33.8m children become infected with RSV each year and that 99 per cent of RSV-related deaths occur in developing countries.
The team hopes that by identifying the numbers affected by the virus, they may contribute to the development of a vaccine against the infection.
Dr Harish Nair, of the University of Edinburgh's Department of Population Health Studies, said: "Our greatest hope of fighting this virus is to develop a vaccine, but before we can implement an immunisation programme, we need to understand exactly how big a problem RSV poses.
"This is the first time we have gathered information on such a global scale and is the best estimate we have for the number of children dying each year from this preventable illness."