The research, published in this month's American Journal of Respiratory and Critical Care Medicine, was a joint project between Imperial College London, St Mary's Hospital, London and the Ruhr-Universitat Bochum, Germany.

Professor Peter Openshaw, from Imperial College London and St Mary's Hospital, and one of the papers authors, comments: "These studies show that RSV is a 'hit and hide' virus, rather like HIV, herpes or some hepatitis viruses. The symptoms seem to go away but the virus is just hiding, waiting for a chance to re-emerge and begin infecting other people."

The researchers infected mice with the human RSV, and found that after 14 days, the virus could no longer be found in samples taken from the airways, but tell-tale traces of the virus's genetic material (viral RNA) were still found lying dormant in lung tissue over 100 days later.

The team believes that this may also be the case in humans, and that long after the initial symptoms, such as coughs and sneezes, have disappeared, the virus could lie dormant in the body. It is possible that the recurrent wheezing which occurs in children who have suffered from bronchiolitis may be due to virus hidden in the lung.

Professor Openshaw says: "Some people may be 'carriers', able to act as a source of new outbreaks in children. If RSV is a 'hit and hide' virus, this could explain where this virus goes in the summer and where it comes from each winter. If the virus is able to lie dormant in previously infected individuals, it could re-emerge when the conditions are right and cause the outbreaks that fill our children's wards each winter."

RSV is very common infecting most children during their first year of life and for some infants RSV leads to bronchiolitis, one of the major causes of infant hospitalisation in the Western world. Around 40 percent of infants who experience bronchiolitis as a result of RSV infection are subsequently affected by recurring wheeze and up to a third can also suffer with childhood asthma.

This research was supported by grants from the Wellcome Trust and the Bundes Ministerium fur Bildung and Forschung.