Public health experts worry about flu and coronavirus overlap

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A member of medical staff takes coronavirus test samples of a woman during drive-thru coronavirus disease (COVID-19) testing, on a converted ice rink.

In the Northern Hemisphere, flu season gets going in the fall and picks up in the winter months.

Viruses, especially ones that are respiratory in nature, generally spread better in the cold. People tend to be indoors more, together in groups — and schools are a major source of transmission.

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Because the flu comes around every year, our bodies may have a familiarity with it, or a “residual immunity,” according to Cécile Viboud, who has been monitoring the virus for decades at the Fogarty International Center at the National Institutes of Health in Maryland.

Still, the virus changes each year, with new strains, she says — that’s why vaccines are so important.

“What we’ve learned over many years is that the flu always surprises us. I mean, the virus evolves so there’s always a part that’s unpredictable.”

Cécile Viboud, Fogarty International Center 

“What we’ve learned over many years is that the flu always surprises us,” Viboud said. “I mean, the virus evolves so there’s always a part that’s unpredictable.”

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And this year, the coronavirus brings a whole new set of challenges. It’s unclear what will happen in the fall and winter, but Viboud and many other public health officials worry about having to deal with two epidemics at once.

While the flu is serious, the new coronavirus is more severe and has no vaccine. It’s a completely new virus to humans, meaning that people young and old are all susceptible to it. The new coronavirus does not appear to follow seasonal patterns, either, and hasn’t calmed down during the warmer months. In just one day a couple of weeks ago, the World Health Organization tallied some 275,000 new cases and nearly 7,000 new deaths.

In the meantime, the impact of co-infections of the flu and the coronavirus is unknown. The coronavirus may also thrive in winter months. Some modelers and public health leaders anticipate more pronounced outbreaks of the coronavirus and bigger surges come fall and winter.

Robert Redfield, the director of the US Centers for Disease Control and Prevention, has warned that the confluence of COVID-19 and the flu, which sometimes shows similar symptoms, could further strain an already limited health care system and have serious implications overall.

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In an interview with WebMD, he said that if people don’t follow public health guidance — wearing masks, social distancing and getting flu shots — the country could see “the worst fall, from a public health perspective, we've ever had.”

Dr. Maria Van Kerkhove, WHO's COVID-19 technical lead and an infectious disease epidemiologist, stressed the importance of getting a flu vaccine this year.

“It will be quite difficult if somebody is infected with either COVID-19 or the flu and they have a flulike illness or cold-like symptoms. We won't be able to distinguish immediately between whether somebody has flu or whether somebody has COVID-19.”

Dr. Maria Van Kerkhove, WHO, COVID-19 technical lead and an infectious disease epidemiologist

“It will be quite difficult if somebody is infected with either COVID-19 or the flu and they have a flulike illness or cold-like symptoms,” Kerkhove said in a recent press conference. “We won't be able to distinguish immediately between whether somebody has flu or whether somebody has COVID-19.”

At the same time, researchers are also paying attention to the flu season already underway in the Southern Hemisphere. In parts of Australia and South Africa, “There’s very little viruses except for COVID-19,” Viboud said.

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She has some strong theories as to why: People’s behavior during the pandemic has changed, making it harder for the flu to spread. The flu also has to hitch a ride to spread from place to place, and there’s just less travel right now because of the pandemic, she says.

Still, many spots in the Southern Hemisphere are wrestling with big outbreaks of the coronavirus.

John Padget, a longtime flu tracker at the Netherlands Institute for Health Services Research, theorizes that it may be in part to something called “viral interference,” a phenomenon where one virus tends to dominate, and in doing so, basically buffers other viruses from taking hold. This has to do with immune activity in our bodies — it’s like a dance, he said.

“The idea is that you don’t get all the viruses circulating at the same time,” and at some point, the other virus might then step in and have its turn, Padget said.

Although Viboud is cautiously optimistic about flu season based on what she’s seeing in the Southern Hemisphere, she cautions that the new coronavirus represents uncharted territory. 

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