Scientists have found evidence to suggest that a type of cold virus, which is common in babies, can lurk in the body for months or even years.
RSV infects most babies within their first year of life
Up until now, scientists have thought that the respiratory syncytial virus (RSV) could only survive for a few days.
But tests on mice show it can hide in the body before striking again.
The findings, published in the American Journal of Respiratory and Critical Care Medicine, may explain why so many catch the virus each year.
RSV is very common. Most children catch it within their first year of life.
For some children, it is very serious. It can cause bronchiolitis or inflammation of the lower passages in the lungs, which can make it difficult to breathe.
About 40% of infants who develop bronchiolitis go on to suffer recurrent wheezing. Up to a third can go on to develop asthma.
Scientists at Imperial College London and the Ruhr-Universitat Bochum in Germany, who carried out this latest study, believe their findings may explain why so many children go on to develop these problems.
The scientists infected mice with the human strain of RSV. Tests showed that after 14 days the virus could no longer be found in samples taken from their airways.
This would normally be taken as a sign that the virus had cleared. However, further tests showed that the virus's genetic material was still present in lung tissue over 100 days later.
The scientists said the findings suggested that RSV was a "hit and hide virus", which means it can lurk in the body before striking again.
"These studies show that RSV is a 'hit and hide' virus, rather like HIV or some hepatitis viruses," said Professor Peter Openshaw of Imperial College and one of those involved in the study.
"The symptoms seem to go away but the virus is just hiding, waiting for a chance to re-emerge and begin infecting other people."
'Hit and hide'
Professor Openshaw said the findings may explain why the virus is able to infect so many children each year.
"If RSV is a 'hit and hide' virus, this could explain where the 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."
Professor Ronald Eccles, director of the Common Cold Centre at Cardiff University, welcomed the study.
"This is a very interesting idea," he told BBC News Online. "Up until now, it has been thought that these viruses come into the body and then go out.
"There have been calls in the past for a vaccine to protect against RSV, because of the serious potential it has in infants especially.
"We don't have a vaccine as yet but perhaps this study will prompt new research in this area."