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The United States is experiencing an exceptionally severe flu season, with hospitalization rates exceeding those witnessed during certain peaks of the Covid-19 pandemic.

Alongside the flu itself, healthcare professionals are noting a significant uptick in patients suffering from severe complications associated with the virus.

In pediatric cases, experts report an increase in hospitalizations due to serious neurological complications, including a particularly severe type of brain swelling known as acute necrotizing encephalopathy (ANE), which can lead to tissue destruction.

Among adult patients, there is a concerning rise in pneumonia cases caused by flesh-eating bacteria, often known as superbugs.

“We’re encountering a lot of necrotizing MRSA pneumonia following influenza, which results in substantial lung tissue damage,” explains Dr. John Lynch, an infectious disease expert at UW Medicine.

Methicillin-resistant Staphylococcus aureus (MRSA) is a bacteria that is resistant to many antibiotics and can cause severe, potentially life-threatening infections. Survivors of this type of pneumonia may suffer long-term lung damage, impacting their overall respiratory function.

Bacterial pneumonia often develops after influenza, particularly in older populations. Doctors suggest this year’s high volumes of cases are attributed to the unusually busy flu season, which remains a cause for concern.

On social media platforms, critical care nurses have described intensive care units brimming with flu patients who have advanced to pneumonia and respiratory failure.

“We’re seeing many patients in their 40s being severely affected by the flu,” a nurse from Maryland shared on Reddit.

“It feels reminiscent of the Delta Covid wave,” remarked another nurse from the Pacific Northwest, though CNN could not independently verify their claims.

The intensity of this flu season is impacting many regions across the country.

According to CDC data for the week ending February 1, there were 14.4 flu hospitalizations for every 100,000 people in the U.S., slightly surpassing hospitalization rates observed during the highest intensity of the Delta outbreak in September 2021.

While flu hospitalization rates this season remain about half of what they were during the Omicron wave in 2022, it marks the first time cumulative flu hospitalizations have exceeded those for Covid-19.

This season has recorded approximately 64 flu hospitalizations per 100,000 individuals, contrasted with around 44 Covid-19 hospitalizations. Last year, Covid-19 cases resulted in nearly two and a half times more hospitalizations than the flu.

Furthermore, weekly flu-related deaths have now outnumbered those attributed to Covid, with the CDC reporting 1,302 flu fatalities in the last two weeks of January, compared to 1,066 Covid deaths.

Nationwide, flu cases are currently at very high levels, with about one in three individuals tested for the flu in clinics or hospitals receiving a positive result.

In some Washington clinics, as many as 50% of tested patients are returning positive results, according to Dr. Lynch.

“A 50% positivity rate is exceptionally high,” he remarked. “It’s astounding.”

Recently, Dr. Keith Van Haren, a pediatric immuno-neurologist at Stanford Medicine, noted a potential spike in ANE cases and is actively seeking information through a platform run by the International Society for Infectious Diseases.

It’s important to note that healthcare professionals are not mandated to report ANE cases to health authorities, which makes tracking trends challenging.

However, Dr. Van Haren and his colleague Dr. Andrew Silverman have discussed the noticeable increase in severe flu cases among children. Reports from their team indicate approximately 35 to 40 ANE cases identified over the past two flu seasons, with most occurring this season.

“Something unusual is happening,” Van Haren stated. “What we are seeing is really different from previous years.”

ANE involves brain swelling that can arise from various viral infections, including the flu, with studies indicating a fatality rate of roughly 50% in cases diagnosed.

When the brain swells inside the rigid skull, the outcomes can be catastrophic. ANE specifically targets the thalamus—a region crucial for regulating sleep and wakefulness—resulting in severe drowsiness and difficulty maintaining consciousness in affected children.

“It’s akin to inflating a balloon inside a cardboard box; it can only expand so much before something ruptures,” Van Haren explained.

Regarding the possibility of bird flu contributing to these cases, Van Haren notes, “Currently, it does not seem to be associated with bird flu,” despite sporadic H5N1 cases reported in people working on farms across numerous states.

Dr. James Antoon, a pediatrician at Monroe Carell Jr. Children’s Hospital at Vanderbilt, confirmed that a single case of ANE has been recorded there this year.

Beyond ANE, Antoon has observed an uptick in various neurological complications in children with flu, including instances of seizures.

However, it remains premature to determine if these occurrences exceed expected figures.

In a typical flu season, roughly four seizure cases are expected for every 10,000 children under 5 who contract the illness. Encephalopathy is even rarer, affecting about one in every 100,000 children with the flu, which, while seemingly small, accumulates significantly when considering millions of flu cases.

“As flu cases rise, we can expect to see an increase in complications,” Antoon explained. “During a challenging season like this, more neurological issues should be anticipated.”

Hospitals are Full and Busy

Dr. Ryan Maves, a critical care medicine specialist at Wake Forest University School of Medicine, compared the current flu season’s intensity to that of the 2009 influenza pandemic, which was caused by the novel H1N1 virus that spread rapidly across the globe.

“In terms of patient volume, our hospital is full,” Maves stated. “While we are not overflowing into the parking lots, the hospital is at capacity, and we are witnessing conditions not seen in years, including adult cases requiring ECMO (extracorporeal membrane oxygenation)—a technique where machines temporarily perform the work of the heart and lungs to facilitate recovery.”

“Every few years, we encounter a particularly troublesome strain of influenza,” noted Dr. Buddy Creech, a pediatric infectious disease specialist at Vanderbilt University Medical Center.

This season, both H1N1 and H3N2 influenza A strains are circulating simultaneously in significant numbers, which is an unusual occurrence.

“Often, we observe a dominant strain, but currently, the prevalence is nearly equal,” Dr. Jennifer Nayak, a pediatric infectious disease specialist at the University of Rochester Medical Center, elaborated. “This is not typical.”

Compounding the situation, less than half of the population, including both adults and children, have been vaccinated against the flu this year.

Approximately 44% of adults have received their flu shots—a rate that has remained relatively unchanged in recent years. Vaccination coverage among children has dropped nearly 14 percentage points, falling from 58% pre-pandemic to 44% this year.

This decline in vaccination rates is alarming to medical professionals.

This flu season has already claimed the lives of 57 children, a number deemed high for this time of year by experts like Nayak. Most of the deceased had not been vaccinated.

“Typically, we see between 100 and 150 children die from influenza annually in a regular year,” Creech remarked. “This is a devastating statistic, especially in light of the availability of vaccines that could prevent such tragic outcomes.”

With both influenza strains present in similar proportions, Creech mentioned that some patients have contracted one strain, recovered, and then fallen ill with the other just weeks later.

“Immunity to one strain does not confer protection against the other in any lasting manner,” he explained. “This is precisely why vaccination is essential; we cannot predict which strain will circulate next.”

Importantly, Creech clarified that the vaccine does not guarantee complete immunity from flu infections.

He shared that he received the vaccine this year yet still contracted flu last week, although his symptoms were “much milder” than what he experienced during the 2009 outbreak before the H1N1 vaccine was available—during which his fever reached 104 degrees Fahrenheit, and his son’s peaked at 106 degrees.

If this news leaves you feeling powerless, there are proactive steps you can take to minimize the risk of severe flu illness.

If you haven’t yet received your flu vaccine, it’s not too late, according to Creech.

“Getting vaccinated now provides a significant boost to your immune response in about a week to ten days,” he noted.

Experts predict at least another month to six weeks of heightened flu activity before conditions improve. Additionally, there is a possibility of an increase in influenza B cases, leading to a spring surge.

“At present, we’re facing a surge of H1N1 and H3N2, and soon we may see influenza B surface, making this an opportune time for vaccination,” Creech indicated.

It remains too early to ascertain how effective this year’s flu vaccine will be against circulating strains. Preliminary studies suggest it may be better aligned with H1N1 strains compared to H3N2 variants.

Therefore, do not rely solely on the vaccine for protection. Enhancing indoor air quality, ensuring proper ventilation, practicing good hand hygiene, and wearing high-quality masks in crowded settings can also reduce your risk of infection.

Lastly, if you do become ill, consider testing yourself. Many pharmacies and grocery stores now offer over-the-counter home flu tests, in addition to those available at medical offices. Antiviral medications may diminish the severity of your illness if taken early.

“The preventive measures discussed for Covid also apply to influenza,” Nayak concluded.

Contributors to this report include CNN’s Deidre McPhillips.