After following Covid-19 safety precautions for several months, everyone braced for a deadly "twindemic" 2020-2021 flu season—but it never came, thanks in large part to behavioral changes aimed at reducing the coronavirus's spread, Jacob Stern writes for The Atlantic.

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The 2020-2021 flu season was a stark contrast to the previous season

Each year, according to Stern, the flu infects roughly 30 million people and kills over 30,000 people in the United States alone. As a result, experts feared that after Covid-19 hit, America would eventually face a twindemic during the 2020-2021 flu season, with both Covid-19 and influenza infecting people.

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However, during the 2020-2021 flu season, the United States recorded around 2,000 cases—17,000 times less than the 35 million reported cases in 2019-2020—and had one known child casualty, compared with 199 pediatric fatalities the previous season.

"We've looked for flu in communities and doctors' offices and hospitals, and we've gotten almost zero," Emily Martin, a University of Michigan epidemiologist, who is part of CDC's flu-monitoring network, said. 

According to CDC, the hospitalization rate for the 2020-21 flu season in America was just 0.7 per 100,000 people—the lowest since the agency started tracking flu data in 2005.

Why the 2020-2021 flu season was virtually nonexistent

Part of the reason for the sudden drop-off could simply be a lack of testing for influenza, as health officials had to focus their resources on addressing Covid-19, John McCauley, director of the Worldwide Influenza Centre at the Francis Crick Institute, said.

However, most of the epidemiologists Stern spoke with emphasized the importance of behavioral changes resulting from Covid-19 precautions, including masking, distancing, remote learning, working from home, and limiting indoor social gatherings. And even though those Covid-19 safety measures weren't consistently enforced in the United States, they helped slow the spread of the coronavirus—and unexpectedly stagnated influenza. 

"This is one of the clear signals that these interventions work," Rachel Baker, who studies public health and infectious disease at Princeton University's High Meadows Environmental Institute, said. "They are really efficient at stopping the spread of these viruses."

We know how to stop the flu—now what?

"But our triumph over the flu also poses a dilemma," Stern writes, in that the country has demonstrated it can save "nearly everyone who dies of the flu"—so long as certain measures are taken. So what does that mean post-pandemic, when Covid-19 safety measures are no longer in place? According to Stern, now that we know how to reduce infection and death from the flu, doing nothing and returning to roughly 30,000 deaths each year without even attempting to save some lives would be irresponsible.

Resource library: How health care organizations can navigate the post-pandemic world

On the one hand, Stern writes, public health experts agreed it would not be "feasible nor desirable" to implement lockdowns each year. He adds that the experts also told him "[b]road restrictions on travel and large indoor gatherings … also seem like nonstarters."

Similarly, even moderate capacity limitations—though beneficial from a health perspective—are "tricky for business," according to Saskia Popescu, an epidemiologist at George Mason University.

However, Seema Lakdawala, a flu-transmission expert at the University of Pittsburgh, suggested organizations could take some partial measures, such as considering rescheduling annual holiday parties for the summer months and hosting those celebrations outdoors.

Linsey Marr, an environmental engineer at Virginia Tech, added that entities could implement a "circuit breaker" system, "in which schools and workplaces could go remote for a week or two to slow flu transmission during severe local outbreaks," Stern writes.

And perhaps most simple of all would be normalizing masking measures. Emory University immunologist, Anice Lowen, said masks are "the low-hanging fruit," since they don't disrupt daily life the way shutdowns or restrictions on indoor gatherings can. 

According to Marr, "we would see huge reductions in colds and flus. No question," if wearing masks in crowded indoor spaces during flu season—or at least when case counts rise—became the norm.

However, Angela Rasmussen, a virologist at the Vaccine and Infectious Disease Organization, warned that even so limited a measure could draw backlash. "[Y]ou're going to have a lot of people who are like, 'Well, we saw this coming. First you mandated masks for Covid,'" she said, "'now you're mandating masks all the time. It's all about control! What about my freedom?'"

Currently, Stern writes, CDC has no plans to endorse any new anti-flu interventions, relying still on the "interim guidance" it published in 2004. That guidance mentions social distancing and school closures as potential "community measures," but emphasizes that no single intervention can provide total protection. In addition, it suggests that only people diagnosed with the flu by a doctor or who have a fever and respiratory symptoms during a known local outbreak should consider wearing a mask.

Speaking on behalf of CDC, David Wentworth, the virology, surveillance, and diagnosis chief within the agency's influenza division, said, "It sounds like we're doing nothing, but really we want to understand what factors have the big impact before you start making those kinds of recommendations." He added, "It's not that we don't care about the tens of thousands of people who are impacted by flu."

For his part, Stern cites policy changes that could make a difference, "[g]iving workers and students the ability to stay home when sick"—although he acknowledges that policy changes alone won't change the problem.

"There's a real culture … that if you're not on your deathbed or you're not going to the hospital, that you're fine to go to work," Rasmussen said. "If you're sick, you should stay home. It seems like a no-brainer, but people are actually really resistant to that."

Ultimately, experts agree that it is unlikely we will be able to consistently repeat the nonexistent 2020-2021 flu season—and, as of right now, flu shots and nonpharmaceutical interventions are the best prevention tool we have. (Stern, The Atlantic, 10/13)