Fifteen children under the age of 15 have now died in the UK from invasive Strep A illness, figures show.
New data from the UK Health Security Agency (UKHSA) shows 13 children under 15 have died in England since September.
Two other deaths of children have been recorded in Belfast and Wales, taking the UK total to 15.
Group A strep bacteria can cause many different infections, ranging from minor illnesses to deadly diseases.
Illnesses caused by Strep A include the skin infection impetigo, scarlet fever and strep throat.
While the vast majority of infections are relatively mild, sometimes the bacteria cause a life-threatening illness called invasive Group A Streptococcal disease.
The UKHSA has said there is no current evidence that a new strain is circulating and the rise in cases is most likely due to high amounts of circulating bacteria and increased social mixing.
Since September, the UKHSA said there have been 652 reports of invasive Strep disease, higher than at the same points over the last five years.
So far this season, there have been 85 cases in children aged one to four, compared 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.
Dr Colin Brown, deputy director of the UKHSA, said: “Scarlet fever and ‘strep throat’ are common childhood illnesses that can be treated easily with antibiotics.
“Please visit NHS.uk, contact 111 online or your GP surgery if your child has symptoms of this infection so they can be assessed for treatment.
“Very rarely, the bacteria can get into the bloodstream and cause more serious illness called invasive Group A strep.
“We know that this is concerning for parents, but I want to stress that while we are seeing an increase in cases in children, this remains very uncommon.
“There a lots of winter bugs circulating that can make your child feel unwell, that mostly aren’t cause for alarm.
“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.”
Figures show that scarlet fever cases remain much higher than normal.
The UKHSA said cases usually show steepest rises in the New Year, but have increased sharply in recent weeks.
So far this season (from September 12 to December 4), there have been 6,601 cases of scarlet fever, more than twice as high as the 2,538 at the same point in the last comparably high season in 2017/2018.
It comes as pharmacists continue to use Twitter to complain of shortages in access to antibiotics, including the liquid version of penicillin, which is often given to children.
Health Secretary Steve Barclay insisted on Wednesday that checks within the Department of Health have not revealed an issue with supply of the medicines.
However, the National Pharmacy Association has pointed to “blips” in the supply chain of liquid penicillin, while the Association of Independent Multiple Pharmacies said pharmacists across the country were struggling to source all they need.