Fact check: COVID-19 pandemic spurred record-low flu activity this season

The claim: There have only been 2,300 cases this flu season

As restaurants and retailers across the nation continue to drop mask requirements for the fully vaccinated following new federal guidance, the importance of masking is being highlighted in one social media post claiming the practice has helped lower flu cases this season.

“I just want to point out that all this ‘useless mask usage and hand-washing’ have also given us the lowest number of flu cases ever recorded,” said Twitter user Tennesseine in a May 14 tweet shared to Facebook on May 19.

The post says there have been only 2,300 flu cases, compared to 38 million cases and 22,000 deaths that supposedly occurred in the U.S. last year.

The post was shared about 10,000 times in the first week after it was posted.

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It’s reasonable to imagine preventative measures against one respiratory illness, such as COVID-19, could confer protection against another like the flu, also known as influenza. But does the figure of 2,300 cases accurately reflect the state of current flu activity in the U.S.?

Possibly, but not exactly.

Number of flu cases is a rough estimate

The 2,300 figure Tennesseine cites is not an exact number, he told USA TODAY.

“The figures are all over the place because the CDC is torturously slow about releasing seasonal data,” he told USA TODAY. “I had to cobble that estimate together from weekly reports, updates throughout the season, etc.”

While the 38 million flu cases and 22,000 deaths is based on 2019-2020 data, one can’t directly compare those numbers to an estimate of this season’s flu cases, said Kate Grusich, a public affairs specialist for the CDC.

“One is an estimate of the burden of influenza based on a mathematical model and the other refers to data reported in the U.S. influenza surveillance report information from the U.S. influenza surveillance system,” she said in an email to USA TODAY.

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Surveillance data may drastically underrepresent the true burden of the flu in the U.S., so statistical models are used to estimate the annual number of cases, hospitalizations and deaths. This was something the CDC could not do for the 2020-2021 season because low flu activity meant there wasn’t enough data to make estimates.

The CDC maintains both sets of numbers because they serve different purposes, Grusich said. Surveillance helps track how the flu is progressing on a week-to-week basis, while the model-based estimates are a more accurate overall representation of the number of cases and deaths.

What if the low number of flu cases just meant fewer people getting tested or diagnosed? That’s likely not the case, said Dr. Lee Riley, professor of epidemiology and infectious disease at the University of California Berkeley’s School of Public Health.

“I think (the number of cases) is still low, because if there were a lot (of flu cases) of epidemic proportions, it would have been recognized,” he told USA TODAY.

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Dr. John Swartzberg, clinical professor emeritus also of UC Berkeley’s School of Public Health, agreed.

“I think we would have seen the typical number of hospitalizations and deaths if we weren’t just diagnosing (influenza),” he told USA TODAY.

COVID-19 preventative response has helped mitigate the flu

Both Riley and Swartzberg agree with what most public health experts now believe: mask mandates and social distancing have helped stifle influenza.

“I’ve been an infectious specialist for 45 years. I’ve never seen anything approaching what we’ve seen this year in terms of the number of influenza cases,” Swartzberg said. “There’s only one major (explanation) that can be reasonably entertained — the nonpharmaceutical interventions we instituted to protect ourselves from COVID.”

Riley said face masks, social distancing and lockdowns all played a role in limiting the spread of the flu.

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“If you go to Asia, especially like Japan during the flu season, almost everybody is wearing masks, and yet they still have epidemics,” he said. “(When COVID-19 happened) they made a real concerted effort to restrict social gathering and contact (tracing). And I think these activities probably had more of an impact on respiratory infections like influenza.”

Riley said it was important to note the lack of influenza now “is not related to any of the anti-COVID-19 measures being taken” but rather seasonality – the U.S. has entered an influenza off-season. The flu peaks between December and February, tapering off as late as May.

Our rating: Missing context

Based on our research, we rate the claim there have been only 2,300 cases of flu this season MISSING CONTEXT, because without additional information it could be misleading. While it’s true public health interventions used to mitigate COVID-19, such as face masks, social distancing and hygiene, have helped to also significantly reduce flu activity, the figure of 2,300 flu cases is an estimate, not an exact number, based on surveillance data publicly provided by the CDC. And the agency cautioned against using surveillance data to represent the burden of the flu nationwide because it does not fully capture every illness that occurs. It also warned against comparing any estimates to past flu season data since those numbers are based on statistical modeling.

Our fact-check sources:

  • USA TODAY, May 20, Home Depot, Costco and more no longer require masks for unvaccinated customers; McDonald’s drops masks Friday
  • Tennesseine, May 14, tweet
  • U.S. Centers for Disease Control and Prevention, Sept. 13, 2019, Key Facts About Influenza (Flu)
  • U.S. Centers for Disease Control and Prevention, Oct. 5, 2020, Disease Burden of Influenza
  • Tennesseine, May 20, Twitter interview with USA TODAY
  • U.S. Centers for Disease Control and Prevention, Oct. 6, 2020, Estimated Influenza Illnesses, Medical visits, Hospitalizations, and Deaths in the United States — 2019–2020 Influenza Season
  • Kate Grusich, May 21, Email interview with USA TODAY
  • Dr. Lee Riley, May 20, Phone interview with USA TODAY
  • Dr. John Swartzberg, May 20, Phone interview with USA TODAY
  • USA TODAY, Dec. 19, 2020, Fact check: Flu activity is low so far likely because of pandemic precautions
  • Mayo Clinic, May 18, How well do face masks protect against coronavirus?
  • U.S. Centers for Disease Control and Prevention, May 6, The Flu Season

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Our fact check work is supported in part by a grant from Facebook.

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