Heard about a lot of people getting flu this winter but not much about covid?
It’s not just you. For the second winter in a row, the United States has faced a punishing flu season, with covid as a more muted threat.
Early in the covid pandemic, coronavirus proved far more transmissible and deadly as it ripped through the world than the flu typically was. Flu was almost nonexistent that first pandemic winter in 2020-2021.
Now that SARS-CoV-2 is no longer a novel virus sweeping through a population with little immunity, covid and influenza illnesses are becoming more similar,with a key difference: Coronavirus circulates year-round and ticks up in the summer, when flu is gone.
Does that mean flu is now the woe of the winter, and covid is the scourge of the summer? It’s complicated and too soon to say.
“We don’t know where covid is going. I really don’t think we know what is the next season going to look like,” said Manisha Juthani, Connecticut’s top public health official and president of the Association of State and Territorial Health Officials.
“But we do know we have an intervention that still helps protect people for both, for flu and covid,” she added, referring to vaccines.
William Schaffner, a professor of infectious diseases at Vanderbilt University, said people should expect variation in the rise and fall of respiratory viruses.
“They don’t all hit home runs,” he said. “But some of them hit triples and doubles and singles, and the individual patient doesn’t care which virus it was that put them in the hospital.”
The numbers this season
The Centers for Disease Control and Prevention estimates25 million have been infected with flu, 330,000 have been hospitalized, and 20,000 have died so far this season.
For covid, the CDC estimatesbetween 3 million to 9 million became ill since October, between 96,000 and 170,000 were hospitalized, and between 10,000 and 30,000 died.
Hospital numbers don’t capture how most people actually experience these illnesses: minor inconveniences or nasty bugs that leave you feeling lousy and homebound. Wastewater tracking, which measures viral particles in sewers to track viral trends, also shows that flu has surged and covid has seen a small uptick, smaller than the summer wave.
“For summer, covid really is the highlight of the story about respiratory disease,” said Marlene Wolfe, an assistant professor at Emory University and program director of WastewaterScan, an organization that tracks diseases through sewage. “Whereas in the winter, we have a more complicated mixture of covid and flu this year peaking at about the same time. That adds an increased burden on the health care setting, and it also results in the possibility of coinfection in individual people who could become more sick if they are infected with both viruses at the same time.”
In last year’s flu season, the CDC estimates 51 million got sick, 710,000 were hospitalized, and 45,000 died — including nearly 300 children, the biggest pediatric death toll since 2009. About 19,000 people died of covidduring that flu season.
Why flu has hit harder
The severity of the last two flu seasons can be explained in part by unusual flu strains.
The H3N2 strain of influenza A, which is typically associatedwith more severe illness in older people, circulating around the world mutated after public health officials selected the strain vaccine manufacturers should target. That left the annual flu shot offering less protection than hoped — similar to what happened last year.
“This mutation is the major reason that we had two big flu seasons in a row, which is very unusual,” Schaffner said.
This is one of the main reasons experts are reticent to say covid will keep playing second fiddle to flu in the winter. Short-term immunity and strains can shift for each disease from season to season.
Covid has to keep changing to keep infecting people. But in the last two years, we haven’t seen the significant leap forward in mutations needed to render immunity to severe illness moot and force hospitals to reopen covid wards. Strains selected for updates to annual covid vaccines have been fairly well matched to the variants circulating in winter the last two years.
“If in 2020 covid was a German shepherd, it’s now a Chihuahua,” said Ziyad Al-Aly, director of the Clinical Epidemiology Center at VA St. Louis Health Care System.
Mutations to the coronavirus since 2020 have left it less adept at causing inflammation and attacking the lungs, said Al-Aly, who is one of the nation’s leading researchers on covid patient outcomes.
Scientists hope this trend continues.
“We have four other coronaviruses that circulate in humans for a long time, and they can be severe, too, in some cases, but usually they do much less damage than SARS-CoV-2,” said Florian Krammer, a virologist and professor of vaccinology at the Icahn School of Medicine at Mount Sinai. “The hope is over time that SARS-CoV-2 will end up as the fifth one that is there but is not doing that much damage.”
Other infectious-disease experts cautioned that it’s not changes in the virus alone that explains the softer bite — humans are changing, too.
Changing immunity
Practically everyone has been infected with the coronavirus or vaccinated against it, leaving bodies much better trained to fight off the virus.
Public health experts worry vaccination rates will slip, especially in the older and very young Americans most likely to become severely ill. Under Health Secretary Robert F. Kennedy Jr., who was an anti-vaccine activist, federal health officials have backed away from full-throated endorsements of both flu and covid immunizations.
The CDC estimates a third of adults ages 65 and older have received the most updated covid vaccine, dropping nine percentage points since last year. More than two-thirds of seniors have been vaccinated for flu, roughly the same as last year.
Jennifer Nuzzo, an epidemiologist and the director of the Pandemic Center at Brown University School of Public Health, said the conditions for serious covid waves are feasible: a rising population of susceptible people as new children are born and are not vaccinated, fewer at-risk people staying up-to-date on shots and mutations to the virus.
“It could take off again,” Nuzzo said. “Will it ever be like 2020? I don’t think so. I think the virus would have to change considerably.”
Which virus is worse?
Early in the pandemic, public health officials often pushed back on people dismissing covid as being just like the flu. Now the two are often lumped together in health messaging.
In a studyof millions of patient records at Veterans Affairs hospitals, researchers found that hospitalization and death rates for covid plunged in the 2024-2025 season, falling below the rates for flu for the first time.
VA patients are disproportionately older White men, making it difficult to generalize the findings.
In Denmark, which has more robust data across its population thanks to a universal health care system, researchers noticed a shiftafter it also experienced a bad flu season and gentler covid winter wave last year. The death rate for covid and flu became similar after the mortality risk from covid was far higher in earlier seasons.
Researchers theorized that the change could be explained by improved cellular immunity for covid, worse cellular immunity for flu — or both.
“They are pretty close to each other — influenza and SARS-CoV-2 — but that doesn’t mean it’s good because influenza is dangerous, too,” Krammer said.
Al-Aly, one of the researchers on the VA study, cautioned against being dismissive of covid.
Unlike influenza, which is primarily a respiratory illness, covid can affect multiple organ systems including the heart, brain and gastrointestinal system. While the lasting complications known as long covid have become less prevalent, they are still a distinguishing feature from the flu.
His research reviewing recordsfor patients 18 months after they were hospitalized for flu before the pandemic or for coronavirus for the first 2½ years of the pandemic found that the covid patients were more likely to die or have long-term complications. It will take more time to see if that pattern holds after the flu-covid numbers flipped.
“If you only look at the dashboards with what’s out there, you will not see the long-term health effects,” Al-Aly said. “You will not see what’s underneath that tip of the iceberg.”
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