In a pandemic era rife with unknowns, here’s another one: What happens when flu season collides with the novel coronavirus pandemic?

The optimistic scenario says shuttered schools and measures like mask wearing and social distancing will keep influenza in check along with COVID-19.

But there’s a bleaker possibility that has health officials pushing for unprecedented levels of flu vaccination this fall.

As cold weather forces people indoors and leads them to lower their guard, both viruses could flourish. The result would be clinics and hospitals crammed with feverish, coughing patients. Medical staff will have to don full protective gear and treat everyone with suspect symptoms as a possible COVID-19 case. Testing supplies will be taxed and people sick with flu or other seasonal bugs could face quarantine until they get a diagnosis.

“I’m worried about the whole kit and caboodle and how confusing it might be,” said UW Medicine’s Dr. John Lynch, director of infection control at Harborview Medical Center. “That’s why getting a flu shot this year is more important than ever — not only to keep you and your family and the community safe from flu, but also to keep people with these other COVID-like illnesses out of doctor’s offices and emergency departments.”

Pharmaceutical companies have boosted production of flu vaccine, and health agencies are gearing up to make vaccine more available and accessible — including for Black, Hispanic, and Native American communities, which are at higher risk from COVID-19 and also less likely to get flu shots.

The Centers for Disease Control and Prevention, which normally distributes about half a million vials for uninsured adults, is buying 9.5 million doses this year, director Dr. Robert Redfield said Thursday. Some of that supply will come to King County, which will be rolling out a campaign in the coming weeks to promote vaccination.

“We believe there will be plenty of flu vaccine available,” said Dr. Jeff Duchin, public health officer for Public Health - Seattle & King County.

With many people working remotely, drugstores are gearing up to fill the gap created by the loss of job site immunization drives. Bartell Drugs ordered 10 to 15% more vaccine than usual, said clinical program manager Christina Ree. To ensure the safety of customers and employees, the local chain added extra disinfection measures and implemented scheduled appointments. Pharmacists will wear protective gear and patients will be whisked in and out without having to stand in line.

Since the novel coronavirus swept across much of the globe at a time when flu transmission was low, little is known about how the two viruses are likely to interact, said Dr. Steven Pergam, infectious disease specialist at the Fred Hutchinson Cancer Research Center and director of infection control for Seattle Cancer Care Alliance.

A few cases of dual infection have been documented around the world, but not much information is available about them, he said. The worry, especially for people with weakened immune systems, is that a double viral whammy could lead to more severe disease.

But there are also hints from studies of other respiratory viruses that some pathogens may compete with each other for the same infectious niche, with one emerging as dominant, Lynch said. No one has any idea whether that might happen with the novel coronavirus and influenza, or which would prevail.

One encouraging sign about the looming viral convergence comes from temperate parts of the Southern Hemisphere, where flu season should be in full swing — but isn’t.

“I’ve never seen anything like this before,” said Lynch, who monitors influenza’s annual global march to help predict how the season might unfold here. “There is essentially no influenza activity anywhere in the world right now.”

The reasons aren’t clear, but it could mean the optimistic scenario is plausible: That steps taken to curb the coronavirus are also working to keep a lid on influenza. Another explanation, though, is that people with flu are simply staying home and avoiding health care systems taxed by the pandemic, an analysis this past week in the Journal of the American Medical Association cautioned.

Whatever the cause, it’s risky to assume flu season will be equally light in the Northern Hemisphere, Lynch said. Many — though not all — of the Southern Hemisphere countries were more diligent about masks, social distancing and other precautions than the United States, he pointed out.

Most viruses have seasonal variations in infectivity, but a summer dip never materialized for the novel coronavirus in the U.S. Instead, infections surged as states relaxed restrictions and lockdown-weary citizens cut loose.

As the weather cools, it’s likely that the virus’s infectivity will increase at least slightly, said Mike Famulare, of the Bellevue-based Institute for Disease Modeling, which was recently incorporated into the Bill & Melinda Gates Foundation. But the main factor controlling whether infections will surge again is people's actions.

“No matter what the seasonality is, behavior, as a society, is still going to be the most important control knob for COVID,” Famulare said.

He and his colleagues haven’t incorporated flu into their models, except as a complicating factor for schools that would have to initially treat all kids with symptoms as if they had COVID-19 — which also underscores the importance of flu vaccination.

In an average year, fewer than half of Americans get flu shots. Redfield hopes to boost that to 65% this year.

Many people don’t bother because the vaccine is only about 40% effective in preventing infection. But it’s highly effective in reducing the severity of disease and preventing hospitalization in people who get infected — which is especially important this season, Duchin pointed out.

Two recent analyses, neither of which has yet been peer reviewed, also raise the intriguing possibility that the flu vaccine might offer some measure of protection against the novel coronavirus.

One study, by researchers from Johns Hopkins University, found COVID-19 mortality rates were lower in counties where higher percentages of people 65 or older got flu shots. The other study analyzed hospital records from nearly 93,000 COVID-19 patients in Brazil and concluded those who were immunized against influenza were 8% less likely to require intensive care and had a 17% lower chance of dying.

"Large scale promotion of influenza vaccines seems advisable, especially in populations at high risk of severe (novel coronavirus) infection," the authors wrote.

But most experts are skeptical.

In the Johns Hopkins study, for example, it’s hard to know whether people in counties where vaccine coverage is high are also more health conscious in general or might have done a better job of social distancing, Pergam said. “I’m not convinced, and biologically it doesn’t make a lot of sense."

Duchin is also wary — though he said he would be “thrilled” if it were true. Some theories suggest general activation of the immune system, as would be triggered by an influenza vaccine, could have an impact on susceptibility to COVID-19, he said — but it’s highly speculative.

“At this stage, it’s just not possible to know with certainty whether influenza vaccine or other infections or what, if anything, in someone’s immunological history or makeup might be either predisposing them to more severe illness or protecting them from more serious infection,” Duchin said.

While flu is not as infectious or deadly as the novel coronavirus, it’s still a dangerous disease, Lynch pointed out. Over the past decade, an average of 134 people a year in Washington have died from confirmed infections, and health officials say the actual number is probably higher. (As of Monday, the state’s COVID-19 death toll stood a 1,867.) Every year, Lynch said, Harborview is crowded with people who have to be hospitalized because of flu.

Pergam urges people to think of the vaccine as a way to protect others as well as themselves — a perspective that’s particularly important this year.

“Flu vaccine is a little bit like wearing a mask,” he said. “It’s not always about you, it’s about everyone around you.”