The number of children under 15 who have died from Strep A in the UK has risen to 15, the UK Health Security Agency has said.
New data for England shows the number of deaths since September has increased to 13.
The other two fatalities were recorded in Wales and Northern Ireland.
Illnesses caused by Strep A include scarlet fever, strep throat, and the skin infection impetigo.
Though most infections are mild, the bacteria can evolve into a life-threatening illness called invasive Group A Streptococcal disease.
Since September, the UKHSA said there had been 652 reports of the invasive form of the disease, which is higher than during the same period over the last five years.
In the current season of Strep A infections, there have been 85 cases in children aged one to four.
That compares to 194 cases in that age group across the whole of the last high season in 2017/2018.
There have also been 60 cases in children aged five to nine. Since September, 60 deaths have been reported across all age groups in England.
The rise in cases is thought to be because of large amounts of bacteria and increased social mixing, the UKHSA added.
There is no current evidence that a new strain is circulating, the agency said.
“There are lots of winter bugs circulating that can make your child feel unwell, that mostly aren’t cause for alarm,” said the deputy director of the UKHSA, Dr Colin Brown.
“However, make sure you talk to a health professional if your child is getting worse after a bout of scarlet fever, a sore throat or respiratory infection – look out for signs such as a fever that won’t go down, dehydration, extreme tiredness and difficulty breathing.”
While Health Secretary Steve Barclay has said there is no shortage of medicines, pharmacists have complained of a lack of antibiotics, including the liquid version of penicillin, which is often given to children.
The National Pharmacy Association has pointed to “blips” in the supply chain of liquid penicillin, while the Association of Independent Multiple Pharmacies said pharmacists were struggling to get hold of all they needed.