Cases peaked in January, however last year saw low numbers due to lockdown.
The charity said a surge in cases could coincide with a large number of Covid-19 infections.
What is syncytial virus?
The respiratory syncytial virus (RSV) is common in babies and children, and almost all children will have had it by the time they are two years old.
The virus may cause a cough or cold.
But for some it can lead to bronchiolitis – an inflammatory infection of the lower airways which can make it difficult to breathe.
The early symptoms of bronchiolitis are similar to those of a common cold but can develop over a few days into a high temperature, a dry and persistent cough, difficulty feeding and wheezing.
Dr Andy Whittamore, clinical lead at the British Lung Foundation, said: “Like most other colds and viruses, RSV starts with a blocked or runny nose and can progress to cause a cough, fever and sometimes breathing difficulties.
“Sometimes a cough might drag on for a few weeks,” he added.
While many cases clear up in two to three weeks, a number of children need hospital admission.
What are the concerns?
The BLF said that RSV is ”rife” and has already seen a 400% rise in calls to its helpline from parents worried about their child having breathing difficulties.
The charity revealed over the past three months an estimated 1,000 children have needed hospital care in England alone.
Dr Whittamore said: “In general practice, we are seeing a lot of children with coughs and viruses that weren’t circulating last year and so their immunity is lowered.
“Doctors on the ground are concerned that alongside a rapid increase in cases of Covid-19, we are also going to see a surge in diseases like bronchiolitis.
How worrying is the virus?
Dr Whittamore reassures parents that “for most children it will be mild and will clear in a few days without any treatment.
It is extremely rare for a well child to die of bronchiolitis, but there are some who will need medical help, although that is still unusual.”
“Some babies do develop severe symptoms with the RSV virus, and warning signs to look out for include if they refuse to feed, are becoming very breathless or if they are breathing in a shallow or irregular way,” he said.
What is the guidance to parents?
The BLF has issued new guidance for parents which includes asking anyone who has a cough or cold to stay away from young children, making sure that anyone who handles their child washes their hands regularly and not smoking around young children and babies.
Dr Whittamore said: “We would advise any parents worried about their child having RSV to speak to their doctor or call our helpline on 03000 030 555. Parents can also visit the British Lung Foundation website.”
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