Ahead of flu season, parents are being warned that healthy children could develop a life-threatening condition after being infected with the virus. 

Over 6 million children contract the flu annually. While most recover without medical intervention, for those under the age of five, approximately 6,000 to 25,000 are hospitalized each year, with 37 to 199 succumbing to the illness.

However, in 2023, there were anecdotal reports from doctors about a rise in acute necrotizing encephalopathy, a severe brain swelling condition that results in fatalities for around 25% of sufferers.

This condition occurs when the immune system excessively reacts to a viral infection, leading to damage to the blood-brain barrier and subsequent brain swelling and tissue damage.

A review published this week in JAMA found there were 41 cases in children across the last two flu seasons, making it ‘extremely rare.’

But three-quarters of those affected were considered healthy, and most were around five years old.

Of the children, all were hospitalized and 11, or 27 percent, died from the disease, with death occurring within three days of symptoms starting.

Only 16 percent of patients had received the flu vaccine, which the CDC recommends children aged six months and older get once a year.

Doctors are raising concerns about acute necrotizing encephalopathy, which can, though rarely, affect healthy children who contract the flu (stock image).

Dr. Nicholas Dragolea, a primary care physician in the UK not associated with the research, shared with DailyMail.com: ‘I see numerous adults and children with the flu each winter.’

‘Acute necrotizing encephalopathy is one of those extremely rare but extremely serious complications that happens predominantly in children.’

This warning is issued in anticipation of the upcoming flu season, generally starting in October, where up to 40 million Americans typically contract the virus annually.

Acute necrotizing encephalopathy is caused by an overreaction from the immune system to a viral infection, most commonly the flu.

This triggers high levels of inflammation in the body that disrupts the blood-brain barrier and causes damage and swelling in brain tissue.

Patients initially suffer from congestion, a cough, diarrhea or fever, but within days they develop fainting, seizures, trouble breathing and difficulty with movement.

Treatment involves anti-viral medications to kill the virus and steroids or anti-inflammatory drugs to calm the immune system.

In the study published in JAMA, researchers contacted 76 academic organizations across the US to ask members to submit reports of cases of acute necrotizing encephalopathy.

Millions of children catch flu every year and most recover without needing medical care (stock image)

They received reports of 41 cases detected between October 2023 and May 2025 from 23 hospitals nationwide.

The patients had an average age of five years old, and three out of four were considered to be healthy and had no previous health conditions. Twenty-three of the patients were female. 

In the group, 38 developed a sudden onset of fever, while 41 patients had encephalopathy, or swelling in the brain, and 28 suffered from seizures.

Eleven of the patients died, or 27 percent.

Among those who were hospitalized, they were on wards for between 11 and 22 days before being discharged.

Of the 38 patients with vaccination history, six were vaccinated against the disease, equivalent to 16 percent.

Children are more at risk from the disease because their immune systems are still developing and may overreact to a virus, causing the complication.

Older people and those with weaker immune systems are also more at risk, as their weaker immune systems raise the risk of an infection that could then cause an overreaction. 

It isn’t clear why there may have been an uptick in cases, but doctors say this could be linked to lockdowns which led to children receiving fewer exposures to ‘good microbes’ which can cause their immune systems to overreact to other infections. 

It comes after the CDC raised the alarm over the condition in March, saying a dozen children had contracted the rare brain disorder.

In a report, it said of the 68 children who died of the flu during the 2024 to 2025 season, nine had encephalopathy and four had acute necrotizing encephalopathy.