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With summer in the rearview mirror, health experts are ramping up their plea for Americans to get the flu shot this fall in an effort to ease the impact of two respiratory illnesses circulating at the same time — an event some have dubbed a “twindemic.”
What the fall and winter will look like — with influenza activity at its peak and Americans still contending with COVID-19 — “remains unknown,” says Costi Sifri, M.D., professor of medicine and director of hospital epidemiology at the University of Virginia. When the coronavirus outbreak started in the U.S., last year's flu season was wrapping up. “So we didn't see how these two viruses or multiple viruses could interact with each other,” he says.
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On the one hand, public health interventions meant to slow the spread of the coronavirus (masks, physical distancing and the cancellation of large gatherings) could make this year's flu season relatively mild, since the two viruses are thought to spread in similar ways.
Countries in the Southern Hemisphere, including Australia and New Zealand, have reported lower levels of flu activity so far this year, but experts caution that doesn't mean the same will hold true in the U.S. “Those countries have had a significant amount of success in social distancing,” which probably helped to weaken flu activity, Sifri says. “Whether we have that experience here is not clear to me.”
One way to improve the chances: the influenza vaccine. Though a flu shot will not prevent a coronavirus infection, experts stress it can help ward off a potentially disastrous winter.
1. Flu vaccine reduces severe illness
Because the two illnesses (flu and COVID-19) are caused by different viruses, experts say it is possible to get infected by both at the same time or sequentially — one right after the other. The effects of a coinfection are still being studied, but early reports show it can be dangerous.
Severe cases of flu or COVID-19 on their own can lead to a life-threatening lung injury, called acute respiratory distress syndrome (ARDS), where fluid leaks into the lungs and breathing becomes difficult. A coinfection with flu and COVID-19 would likely mean “the severity of respiratory failure would be greater,” says Michael Matthay, M.D., professor of medicine at the University of California San Francisco and an expert on treating patients with ARDS. “Or having two illnesses in a row that affected the lungs would make the respiratory failure more severe."
That's where the flu shot comes in. Even if the influenza vaccine fails to prevent the flu (it's between 40 percent and 60 percent effective, according to the Centers for Disease Control and Prevention [CDC]), it reduces the severity of illness in people who get it — meaning it protects flu patients from severe respiratory failure “for the most part,” Matthay says.