Discoveries
What to Expect This Flu Season
Last year, the magnitude of the COVID-19 pandemic overshadowed the absence, for the first time in recorded history, of our usual global pandemic: the flu. That event—or non-event—has left epidemiologists with questions about the 2021 flu season.
From October 2020 to May 2021, Cedars-Sinai didn’t treat a single patient for influenza.
“Not even one, and it’s not for lack of testing—we did lot of tests, it just was not present,” says Dr. Michael Ben-Aderet, director of Hospital Epidemiology.
Every year, the flu pandemic cycles from the Southern Hemisphere to the Northern Hemisphere and back again—but this time, it just disappeared, along with the standard horde of other cold-weather communicable diseases.
“We’re used to seeing a potpourri of respiratory viruses in the winter, but this year we saw only the extremely occasional common cold,” says Dr. Margie Morgan, director of Clinical Microbiology at Cedars-Sinai. “No flu or other respiratory viruses were detected.”
"All the things we thought could help prevent something as wild and contagious as COVID-19—face coverings, distancing—worked really well for viruses we know and understand"
What happened? Experts say the drop is probably at least partially due to widespread wearing of masks, physical distancing, school closures and travel slowdowns—everything meant to disrupt the transmission of COVID-19
“All the things we thought could help prevent something as wild and contagious as COVID-19—face coverings, distancing—worked really well for viruses we know and understand,” Dr. Ben-Aderet says.
It’s possible, too, that our collective immunity to the flu is just stronger than it is to the newer coronavirus.
“We’ve all been through so many flu seasons and rounds of flu vaccinations that we have better immunity, whereas nobody had ever seen COVID-19,” Dr. Ben-Aderet says. “The truth is in there somewhere.”
Additionally, natural selection among the viral community could have whittled the field.
“There’s a theory that only one respiratory virus can have dominance—the way SARS-Cov2 took over our personal airways and the air of the world, maybe that wiped out every other competitive virus,” Dr. Morgan says. “We don’t know the real reasons, but many things probably played a role.”
Though no one missed the flu, its disappearance could have negative consequences for vaccine efficacy. Since the flu virus is a particularly shifty one, constantly evolving to evade our immune systems, scientists tweak the vaccine to target the specific strains they predict will be circulating in a given year. Vaccine development is always an educated guess, based on data from the prior year. But in a year without data, preparing shots for 2021–2022 could be more of a gamble than usual.
What does Dr. Ben-Aderet expect next season?
“On one hand, if we interrupted transmission of the flu, we may have a mild season because there’s not much virus out there,” he says. “On the other hand—where is the reservoir of influenza lurking? After a resurgence in travel after COVID-19 vaccinations, we could get a pretty severe flu season.”
Scientists usually look to August—the end of Australia’s winter—to see how the flu strikes there as a predictor for what we may see come October in the northern hemisphere. This year, again, Australia's flu activity remains historically low—possibly because the country is currently on COVID-19 lockdown.
Epidemiologists anticipate the United States will experience some degree of flu this season. At Cedars-Sinai, the microbiology laboratory is preparing more effective, efficient tests for a combination of viruses that might present this season.
"Every year we track the flu—it’s the No. 1 viral illness. It’s always possible we’ll have another novel outbreak. The flu is out there"
“Influenza, COVID-19 and other viruses that cause colds and infections—their symptoms can be similar but their therapies can differ,” Dr. Morgan says. “We’ll be ready to help clinicians determine patients’ diagnoses so they can treat them effectively.”
It’s not likely we’ll understand what to expect until the flu cycles the globe again—but experts are sure it’s not going anywhere. And even though the worst flu pandemic in recent years doesn’t approach the devastation of COVID-19, influenza is still nothing to sneeze at.
“Every year we track the flu—it’s the No. 1 viral illness,” Dr. Ben-Aderet says. “It’s always possible we’ll have another novel outbreak. The flu is out there.”
