By Ashley Fuoco Antonelli, Senior Editor

Earlier this year, public health experts warned that the United States could face a "nightmare winter" if the nation's coronavirus epidemic collided with a severe flu season. To stave off that scenario, experts called for measures to get America's coronavirus epidemic under control, as well as efforts to prevent a gnarly flu season.

Flu in the Southern Hemisphere has 'practically disappeared.' What does that mean for America's flu season?

So far, America hasn't been able to get the coronavirus epidemic under control, with numbers of new coronavirus cases, as well as related hospitalizations and deaths, skyrocketing in recent weeks. But while many experts projected a "twindemic" as we neared flu season, it turns out the country's flu season—which typically sees growing activity at this point in the season—has been comparatively mild this year.

News of a milder flu season certainly is encouraging. Public health experts say, for instance, that lower rates of flu could help to free up hospital capacity to treat America's increasing number of Covid-19 patients. It also means Americans are less likely to contract the novel coronavirus and influenza at the same time, which possibly could wreak havoc on their bodies.

So why has this year's flu season been comparatively mild? And will that trend continue even as coronavirus hospitalizations rise? Let's take a closer look.

2 reasons why flu season hasn't been terrible—so far

1. Measures intended to curb the novel coronavirus's spread may also be curbing the flu

One reason why the United States could be seeing a mild flu season so far this year is that measures Americans are taking to avoid spreading the novel coronavirus also are helping to curb influenza's spread. Public health experts point to the Southern Hemisphere's relatively mild flu season as evidence of this possibility.

Countries in the Southern Hemisphere—such as Argentina, Chile, and New Zealand—reported lower numbers of flu cases this year compared with previous years—and health officials attributed the decline to widespread coronavirus restrictions such as mask wearing, travel restrictions, and social distancing.

Richard Medlicott, a general practitioner in New Zealand, attributed New Zealand's mild flu season to school closures. Medlicott said his clinic experienced a 90% decline in flu patients and a 60% decline in other respiratory illnesses as of July 2020 when compared with last year. "Children are the main reservoir [of these viruses]," Medlicott said. "They haven't been at child care and that has meant they've had less chance to spread it in the community."

Restrictions on incoming air travel during the Northern Hemisphere's flu season also helped prevent travelers from bringing the flu to the Southern Hemisphere, some health experts believe, as Argentina, Australia, Chile, and New Zealand shut down international arrivals in March.

"Strict border restrictions and alert-level-based response including social distancing measures has had an impact," said Sarah Jefferies, a public-health physician at New Zealand's Institute of Environmental Science and Research.

But why have these measures been effective against the flu and not the new coronavirus? CDC notes existing evidence suggests that while the influenza virus and the new coronavirus spread in similar ways (from person-to-person via close contact), there are key differences between the two viruses that could make influenza more responsive to the public health measures. For instance, CDC notes that the novel coronavirus "is more contagious among certain populations and age groups than flu"; that individuals infected with the coronavirus may be contagious longer than those with the flu; and that people infected with the coronavirus may have no or delayed symptoms, so they may not be aware that they're infected.

2. More Americans may have gotten flu vaccines this year

Another possible reason why the United States' flu season has been comparatively mild so far this year could be that more Americans have gotten vaccinated against influenza when compared with previous years.

Pharmacies this year have reported seeing record demand for flu shots. Jocelyn Konrad, Rite Aid's chief pharmacy officer, recently told Reuter's Caroline Humer, "Right out of the gate, we saw much more volume [for flu vaccinations] than last [year]."

According to Humer, Rite Aid has reported seeing a 40% increase in demand for flu vaccinations when compared with last year, and Walmart has seen demand for flu shots double over last year. Similarly, CVS Health said it expects to administer 18 million flu shots this season—up from nine million last year. And a Walgreens spokesperson told Human that the company's U.S. stores are doling out 50% more flu vaccinations this year than in 2019.

However, it's possible that not all of that increased demand is coming from patients who didn't get vaccinated last year. Some of the patients seeking flu shots at retail pharmacies this year could be using the venues as an alternative source for their vaccination, which they usually would get at a doctor's office or through a clinic set up at their workplaces, for example.

2 reasons why flu season could take a turn for the worse

1. The flu could be more rampant in America than data currently suggests

CDC has warned that its data on flu activity in the United States so far could be inaccurate because of America's coronavirus epidemic. CDC in its Weekly U.S. Influenza Surveillance Report notes, "[H]ealth care-seeking behaviors have changed dramatically during the Covid-19 pandemic. Many people are accessing the health care system in alternative settings which may or may not be captured as a part of [CDC's data]. Therefore, [CDC's] data … should be interpreted with extreme caution."

2. Flu season typically starts to worsen around Thanksgiving—and could be tied to how well Americans follow coronavirus mitigation measures

While America typically sees higher flu activity at this point in the year than it is currently, flu activity in the country also usually accelerates around Thanksgiving—meaning we could start to see influxes.

As the Philadelphia Inquirer's Stacey Burling explains, "Flu typically starts off slow in October and November, picks up speed around Thanksgiving, picks up more speed after the December holidays and peaks in January and February."

Why? Because people tend to gather more over the holidays, which means there are more chances for people to transmit the flu to others.

That may hold true this year, as well, but just how much the country's flu season peaks over the holidays could be tied to how well Americans follow coronavirus mitigation measures. As noted above, mask wearing, hand washing, and social distancing appear to have curbed flu season in the Southern Hemisphere—and those practices might be doing the same in the United States.

But those effects could be minimized if a large number of Americans gather indoors over the holidays with people who don't live in their households, especially if they do so without wearing masks. And experts have noted that, when compared with countries in the Southern Hemisphere, the United States has implemented substantially fewer restrictions intended to curb the virus's spread—and Americans have been less apt to follow the restrictions that are in place when compared with residents in other countries.

Ultimately, flu season is hard to predict—so get your flu shot, experts say

Overall, there's one key thing to keep in mind: Flu season is particularly hard to predict, experts say.

"Flu is fickle," William Schaffner, an infectious diseases specialist at Vanderbilt University Medical Center, told the Inquirer's Burling. As Burling explains, flu season sometimes can "star[t] late or [have] more than one peak."

So public health experts' message remains the same: Get your flu shot if you haven't yet done so. "This is a critical year for us to try to take flu as much off the table as we can," CDC Director Robert Redfield has said, warning that, otherwise, "[o]ur hospital capacity could get strained."

Also, wear a mask, wash your hands, and social distance—both to stop the flu and to help get the novel coronavirus under control, experts say.