Flu epidemic in the US is unusual, surpassing the Covid-19 pandemic

Doctors have recorded many flu patients in the US experiencing dangerous complications. Children suffer neurological complications such as brain swelling causing tissue death (acute necrotizing encephalitis - ANE). Adults suffer from pneumonia caused by the "flesh-eating" super bacteria.

'Many cases of MRSA (methicillin-resistant Staphylococcus aureus) pneumonia are severe, causing destruction of lung tissue,' said Dr. John Lynch, an infectious disease specialist at UW Medicine. MRSA is a type of bacteria that is resistant to many antibiotics. The infection can be fatal, and survivors can suffer lung scarring, reducing their ability to breathe normally.

Bacterial pneumonia often occurs after the flu, especially in older adults. Doctors say the increase in cases is due to a severe flu season. On social media, intensive care nurses said that the wards were overloaded with patients with severe flu, pneumonia and respiratory failure.

Flu season surpasses Covid-19

From January 23 to February 1, 14.4 people per 100,000 Americans were hospitalized with flu, higher than the Covid-19 hospitalization rate during the peak of the Delta wave in September 2021, according to the US Centers for Disease Control and Prevention (CDC).

Hospitalization rates are half of the peak of Covid-19 during the 2022 Omicron wave, but this is the first flu season with cumulative hospitalizations higher than Covid-19. About 64 flu hospitalizations per 100,000 people as of 1/2, compared with 44 for Covid-19. Last season, Covid-19 hospitalizations were 2.4 times higher than flu.

The number of weekly flu deaths also surpassed Covid-19 deaths for the first time. The flu killed 1,302 people in the last two weeks of January, compared to 1,066 people who died from Covid-19. According to the CDC, flu activity is high nationwide, with one in three people tested positive in a clinic or hospital.

In some Washington clinics, 50% of patients tested positive, a number that Dr. Lynch said was 'staggering, surpassing previous Covid situations.'

Flu cases in the US are at a 15-year high. Photo: CBS

Children with brain complications after flu​ ​​​​

Dr. Keith Van Haren, a pediatric neuroimmunologist at Stanford Medicine, reported a sharp increase in cases of acute necrotizing encephalitis (ANE) in children with influenza. Doctors are not required to report ANE cases to public health agencies. There is also no official annual data in the United States, making it difficult to track trends. However, in discussions with Dr. Van Haren and his colleague Andrew Silverman at Stanford, they said their team has seen 35 to 40 cases of ANE over the past two flu seasons at university hospitals, most of them this season.

'Everything that is happening is unusual,' said Dr. Van Haren.

Research shows that ANE has a mortality rate of about 50%. The brain swells within the rigid skull and can be fatal. In ANE patients, the swelling causes tissue death in the thalamus, which controls sleep and wake cycles. Children will experience intense sleepiness and difficulty staying awake.

In addition to ANE, experts have also noted other neurological complications in children with influenza, such as seizures. However, it is too early to say whether the current flu cases are unusually high. In a typical flu season, four out of every 10,000 children under the age of five who get the flu have seizures. Encephalitis (brain swelling) is rarer: about one in 100,000 children. This is a small number, but it becomes much larger when multiplied by the millions of current flu cases.

Hospital overload​ ​

Dr. Ryan Maves, an emergency medicine specialist at Wake Forest University School of Medicine, said the intensity of the 2025 flu season is similar to the 2009 flu pandemic, caused by the novel H1N1 virus that emerged in Mexico and quickly spread globally.

"The hospitals are full. Patients aren't spilling out into the parking lot like they were during the pandemic, but the clinics are very busy. We're seeing things we haven't seen in years, like older people needing ECMO to recover," said Dr. Maves.

Every few years, the United States experiences a severe strain of flu, explained Dr. Buddy Creech, a pediatric infectious disease specialist at Vanderbilt University Medical Center in Nashville. This year, two strains of influenza A (H1N1 and H3N2) are causing illness, and unusually, they are occurring in roughly equal proportions. Dr. Creech said some patients have been infected with one strain, recovered, and then infected with the other strain just a few weeks later.

"Normally one strain would be dominant, but right now it's almost 50/50. That's not something we see often," said Dr. Jennifer Nayak, a pediatric infectious disease specialist at the University of Rochester Medical Center.

At the same time, less than half of adults and children have received a flu shot this year. About 44 percent of adults have been vaccinated, a rate that has held steady over the past few years. Vaccine coverage among children has dropped nearly 14 percentage points, from 58 percent before the pandemic to 44 percent. The trend has doctors worried.

It is too early to know how well this year's flu vaccine protects against circulating strains. Some preliminary tests suggest the vaccine is more effective at protecting against H1N1 than against the circulating H3N2 variant.

Samuel Daniel

Update 18 February 2025