The US is in the throes of an unusually intense and severe flu season, with hospitalization rates topping the levels seen with Covid-19 at some points of the pandemic.
On top of the flu infection itself, doctors say they’re seeing large numbers of patients with some of its most devastating complications.
In children, specialists say they’re seeing more than usual come to the hospital with neurologic complications, including devastating brain swelling that leads to tissue death — a condition called acute necrotizing encephalopathy, or ANE.
In adults, there are unexpected levels of pneumonia caused by flesh-eating superbug bacteria.
“We’re seeing a lot of MRSA pneumonia and really bad MRSA pneumonia after influenza, so what we call necrotizing, where you’re getting a lot of destruction of the lung tissue,” said Dr. John Lynch, an infectious disease specialist at UW Medicine.
MRSA is methicillin-resistant Staphylococcus aureus, a type of bacteria that shrugs off a lot of the antibiotics available to treat it. The infection can be deadly, but a person who survives this kind of pneumonia may also have scarred lungs, diminishing the ability to breathe normally during everyday activities.
Bacterial pneumonia infections commonly follow the flu, especially for older adults. Doctors think they’re seeing more of these cases this year simply because the season is so busy. Still, they say, it’s unsettling.
On social media, people who identified themselves as critical care nurses say their intensive care units are packed with sick flu patients who’ve progressed to pneumonia and respiratory failure.
“We’re getting so many people in their 40s just absolutely getting wrecked by the flu,” one person who described themself as a nurse from Maryland wrote on Reddit.
They’re not the only places getting hit hard.
During the week ending February 1, there were 14.4 flu hospitalizations for every 100,000 people in the US, slightly higher than the rate of Covid-19 hospitalizations during the height of the Delta wave in September 2021, according to data from the US Centers for Disease Control and Prevention.
Flu hospitalization rates this season are still about half of what they were during the very peak of the Covid pandemic, in the Omicron wave in 2022 – but it’s the first season that there have been more cumulative hospitalizations for flu than for Covid.
There have been about 64 flu hospitalizations for every 100,000 people so far this season, according to CDC data through February 1, compared with about 44 Covid hospitalizations for every 100,000 people. Last season, there were about 2.4 times more hospitalizations for Covid than for flu.
Weekly deaths from flu have also surpassed those from Covid for the first time, CDC data shows. There were 1,302 deaths from flu in the last two weeks of January, compared with 1,066 deaths from Covid.
From coast to coast, flu activity is very high, according to the CDC, with about 1 in every 3 people who are given a flu test in a clinic or hospital getting a positive result.
At some clinics in Washington, as many as half of patients who are tested are positive, Lynch said.
“Fifty percent positivity is really high,” he said. “Really mind-blowing.”
Doctors warn of brain complications in kids
This week, Dr. Keith Van Haren, a pediatric immuno-neurologist at Stanford Medicine, posted a request for information on ANE cases to a service run by the International Society for Infectious Diseases, wrote that he and others in parts of the US have noted what appeared to be a sharp increase in cases this year.
Doctors are not required to report ANE cases to public health departments and there’s no official tally of the typical number that are reported year-to-year, so it’s hard to tease out trends.
In discussions with his colleagues, however, Van Haren and his Stanford colleague Dr. Andrew Silverman are hearing about an increase in severe flu cases in children. Members of his team say they’ve heard of about 35 to 40 ANE cases over the past two flu seasons at university hospitals, and Silverman said most of those have been this season.
ANE is brain swelling that may occur as the result of a number of viral infections, including the flu. Studies suggest that it’s fatal in about half of cases.
When the brain swells inside the hard shell of the skull, it can have devastating consequences. With ANE, the swelling results in the death of tissue in a specific area called the thalamus, which controls sleep and wakefulness. Children who have this complication develop intense drowsiness and have a hard time staying awake.
“It’s sort of like blowing up a balloon in a cardboard box. It can only expand so much before something breaks,” Van Haren said.
Van Haren says he knows that the next question is whether this could involve bird flu. Cases of H5N1 bird flu have been sporadically reported in humans in a dozen states, mostly in people who work on farms. “It does not appear to be bird flu,” he said.
Dr. James Antoon, a pediatrician at Monroe Carell Jr. Children’s Hospital at Vanderbilt, said workers there have seen one case of ANE this year.
Beyond ANE, Antoon said they’ve noticed an increase in a range of neurologic complications in children with the flu, including seizures.
It’s too early to say whether these are outside the numbers they would expect, though.
In a typical flu season, Antoon said, they might expect to see four cases of seizures for every 10,000 children under 5 who have the flu. Rates of encephalopathy, or brain swelling, are even rarer: about 1 for every 100,000 children with the flu, he says. Those numbers sound small, but when multiplied over millions of flu cases, they add up.
“We expect there to be more complications when we have more cases of influenza,” Antoon said, “and so we would expect, with a bad in the season like this, to see more neurologic complications.”
Hospitals are full and busy
Dr. Ryan Maves, a critical care medicine specialist at Wake Forest University School of Medicine, said the intensity of this flu season feels like the 2009 influenza pandemic, which was triggered by a new virus, H1N1, that emerged in Mexico and rapidly spread worldwide.
“In terms of the sheer volume in the hospital, I mean, the hospital is full,” Maves said. “We’re not spilling into the parking lot, but the hospital is very full, and we’re seeing things that I hadn’t personally seen in a few years,” such as adult patients who need ECMO, or extracorporeal membrane oxygenation therapy, with which machines take over for the work of the heart and lungs to buy the body time to recover.
“We have this happen every few years, where we have a particular strain of influenza that is challenging for us,” said Dr. Buddy Creech, a pediatric infectious disease expert at Vanderbilt University Medical Center in Nashville.
This year, two influenza A strains are causing misery — H1N1 and H3N2 — and what’s unusual is that they seem to be sharing the stage in roughly equal amounts.
“A lot of times, you see a strong predominance of one or the other, and right now it’s split nearly 50/50,” said Dr. Jennifer Nayak, a pediatric infectious disease specialist at the University of Rochester Medical Center. “It’s not the typical thing that we see.”
At the same time, fewer than half of adults and children have had a flu shot this year.
About 44% of adults have been immunized against the flu, a level that’s stayed steady for the past several years. Vaccine coverage for kids has dropped by nearly 14 percentage points, falling from 58% before the pandemic to 44% this year.
That’s a trend that worries doctors.
This virus season, 57 children have died from the flu. “That’s relatively high for this time of year, for sure,” Nayak said. Most of them have been unvaccinated.
“Keep in mind that every year, somewhere between 100 and 150 children die of influenza, and that’s just in a regular run-of-the-mill year,” Creech said. “That’s a devastating number when we have a vaccine that can prevent those severe outcomes.”
With two strains circulating in roughly equal amounts, Creech said he’s heard of patients infected with one strain of the flu who recover, only to catch the other just a few weeks later.
“Immunity to one of them does not give you immunity to the other in any sort of durable way,” he said. “This is why we vaccinate, because you don’t know which flu you’re going to be exposed to.”
To be clear, Creech said, the vaccine won’t keep you from catching the flu.
Creech got his shot this year and still had influenza last week. But his infection was “way more mild” than the flu he had in 2009, before the H1N1 vaccine was available. That time, his temperature hit 104 degrees Fahrenheit, and his son’s was 106.
There’s still time to protect yourself
If you’re reading this news and feeling helpless, don’t. There are things you can do to lower your risk of a bad case of the flu.
First, if you forgot your vaccine, there’s still time to get one, Creech said.
“If you get it right now, it takes about a week for an adult, maybe 10 days, for there to be a really good boosting of the immune response,” he said.
Experts anticipate at least another month to six weeks of bad flu before things get better. Even then, it’s not uncommon to see a bump in flu B, which leads to a spring peak.
“So right now, we’re seeing a truckload of H1N1, we’re seeing this H3N2, and now influenza B is going to come around for a spring meet and greet, so now is a reasonable time to do it,” Creech said.
It’s too early to know how completely this year’s flu vaccine protects against the circulating strains. Some preliminary testing, in which viruses from patients put in a test tube with blood from vaccinated ferrets, suggest that the vaccine may be better matched to the H1N1 viruses than the H3N2 variants that are floating around.
So don’t rely on the vaccine alone for protection. Cleaning indoor air and ventilating spaces, washing your hands and wearing a high-quality mask in crowded places can help, too.
Finally, test yourself if you get sick. Over-the-counter home tests for flu are available at many pharmacies and grocery stores, in addition to tests at doctor’s offices. Antiviral drugs can lower the risk that your infection will become severe, and they work best if you take them early on.
“All the similar things we’ve talked about with Covid, the same goes true for influenza,” Nayak said.