(Clare Nicholas for The Washington Post)

Doctors and health officials are urging Americans to get vaccinated against influenza in record numbers this fall to avoid a dreaded scenario: flu colliding with a raging coronavirus pandemic.

They worry that tens of millions of ­flu-related illnesses could overwhelm hospitals, doctor offices and laboratories that test for both respiratory illnesses.

Symptoms of flu and covid-19, the disease caused by the novel coronavirus, are similar.

“When someone presents to a physician with fever, cough, malaise, unless it’s one of the few things peculiar to covid-19, like a loss of smell, it’s hard to tell them apart when both are circulating in the community,” said Benjamin D. Singer, an assistant professor of medicine at Northwestern University’s Feinberg School of Medicine and a pulmonary critical care specialist at Northwestern Memorial Hospital.

But the months ahead don’t have to be so difficult. If people follow social distancing measures and wear masks, those measures will limit transmission of covid-19 — and control influenza. Both viruses spread mainly through person-to-person respiratory droplets when a sick person coughs, sneezes or talks.

“This fall and winter could be one of the most complicated public health times we have, with the two coming at the same time,” Robert Redfield, director of the Centers for Disease Control and Prevention, said in a recent interview on the JAMA network.

“On the other hand, I’m an optimist. If the American public heeds the advice that we said about face covering and the social distancing and the hand-washing and being smart about crowds, this could be one of the best flu seasons we have had,” Redfield said. “And particularly if they do one more thing, and that is to embrace the flu vaccine with confidence.

The CDC advises that almost everyone 6 months or older get a flu vaccine annually. It is considered especially important for individuals at risk of severe illness: children younger than 2, adults older than 65, people with suppressed immune systems, pregnant women and anyone with chronic lung, heart, kidney or liver disease.

The flu vaccine is produced by private manufacturers, with a record number of doses being churned out this year — nearly 200 million, up from about 175 million last year. Influenza doses began shipping in July, and production and distribution will occur over a longer period this season — through January or later — to respond to expected increased demand. ​

The CDC has also taken the rare step of buying more than 9 million doses to be distributed to states for adult vaccination. The agency typically buys about 500,000 adult doses. Health officials want uninsured adults who lost their jobs during the pandemic to have increased access to flu shots.

Typically, fewer than half of Americans get a seasonal flu shot. Vaccination rates for Blacks and Hispanics have traditionally been lower, with slightly more than a third of Black and Hispanic adults vaccinated, according to CDC data.

This year, Redfield said, his goal is to boost adult vaccination rates to 65 percent across the board.

“This is a critical year for us to try to take flu as much off the table as we can,” he said in the JAMA interview. In children, vaccination rates are typically about 60 percent. Adult rates hover “in the high 30s,” Redfield said.

In at least one state, Massachusetts, flu vaccination is now required for virtually all students and children, starting in child care through college. Vermont’s health commissioner said that state is considering a mandate for school-age children and expects a decision within weeks.

Federal health officials recently expanded access to flu shots, authorizing pharmacists to vaccinate children ages 3 to 18.

Some experts see hopeful signs in exceptionally low levels of flu in the Southern Hemisphere, which could mean little infection spreading north. Experts cited public health measures put in place in Australia and other countries early in the coronavirus pandemic as helping reduce flu circulation. With less global travel, there may be less global circulation of influenza viruses.

But in the United States, people are exhausted by the pandemic, and their embrace of public health measures varies widely. What’s more, experts don’t know whether the low levels of influenza in the Southern Hemisphere were actually the result of fewer people seeking medical treatment because of pandemic-related restrictions or because they were afraid to leave their homes. That could translate into flu cases going undetected and unreported.

With so little seasonal transmission in the Southern Hemisphere, it’s harder for epidemiologists and virologists to prepare for flu in the Northern Hemisphere and predict the strains likely to circulate.

“We really don’t know what’s been going on there,” said Arnold Monto, professor of epidemiology at the University of Michigan. “People should not assume that because we’re changing our behavior [because of covid-19] that we’re going to see a lighter flu season.”

Monto is worried the predominant flu strain this season could be H3N2, the most feared strain. It’s associated with more complications, hospitalizations and deaths, especially among children, people 65 and older, and people with certain chronic conditions. That was the dominant strain in 2017-2018, when hospitals were overwhelmed and a record 188 children died, according to the CDC.

In the United States, doctors say it is vital to maintain routine medical care during this fall and winter.

“If you let your health suffer, you’re more at risk from covid-19,” Vanderbilt University infectious-disease expert Keipp Talbot said. “If you’re going to be exposed to anyone at all, you need to have a flu shot.”

Even with a record number of flu vaccine doses, Talbot said people should not delay getting their shots. Social distancing and cleaning protocols at pharmacies mean it may take longer. “They’re not doing 50 people in two hours,” she said. “More likely, they’re doing 50 people over three or four days.”

Having flu and covid-19 circulating at the same time could complicate diagnoses and make treatment challenging. Flu can be addressed with antivirals, and the sooner you get treatment, the better, Singer said. Patients with influenza typically experience the most severe symptoms during the first week of illness, while patients with covid-19 may experience symptoms over a longer period of time, with a peak during the second or third week of illness, experts said.

Steroids such as dexamethasone may help covid-19 patients but harm those sick with flu, Singer said.

Some people with covid-19 might mistakenly think they have flu and not take precautions to prevent transmission of the coronavirus, which is deadlier and more contagious. Most people with flu are contagious for about a day before showing symptoms.

Someone with covid-19 may spread the virus for about two days before experiencing symptoms and remain contagious for at least 10 days after symptoms appear. For someone with no symptoms or symptoms that go away, it’s possible to remain contagious for at least 10 days after testing positive for the virus.

It’s possible for people to be infected with both viruses at the same time, although experts say odds of that are small, and data on simultaneous infection are scant. Some findings not yet peer-reviewed suggest that getting a flu shot may be linked to protection against covid-19, according to a recent JAMA article.

Singer, who has been treating covid-19 patients in his hospital’s intensive care unit, is not optimistic about the coming flu season.

“Right now, the number of patients hospitalized with covid-19 in our ICUs is similar to what they would be at the peak of flu season, in February and March,” he said.

Take even a mild flu season, add that to the coronavirus pandemic and “you really begin to start stretching the capacity at the health center level,” he said.

Rhode Island’s successful reopening of child-care programs shows ‘there is a path,’ CDC director says

How these Maine sleep-away camps prevented coronavirus from spreading

Who should get a coronavirus vaccine first?

Coronavirus: What you need to know

End of the public health emergency: The Biden administration ended the public health emergency for the coronavirus pandemic on May 11, just days after WHO said it would no longer classify the coronavirus pandemic as a public health emergency. Here’s what the end of the covid public health emergency means for you.

Tracking covid cases, deaths: Covid-19 was the fourth leading cause of death in the United States last year with covid deaths dropping 47 percent between 2021 and 2022. See the latest covid numbers in the U.S. and across the world.

The latest on coronavirus boosters: The FDA cleared the way for people who are at least 65 or immune-compromised to receive a second updated booster shot for the coronavirus. Here’s who should get the second covid booster and when.

New covid variant: A new coronavirus subvariant, XBB. 1.16, has been designated as a “variant under monitoring” by the World Health Organization. The latest omicron offshoot is particularly prevalent in India. Here’s what you need to know about Arcturus.

Would we shut down again? What will the United States do the next time a deadly virus comes knocking on the door?

For the latest news, sign up for our free newsletter.