FILE - In this Thursday, Jan. 23, 2020, file photo, a patient receives an influenza vaccine in Mesquite, Texas. Amid all the focus on COVID-19 vaccinations, U.S. health experts have another plea: Don't skip your flu shot. With U.S. schools and businesses reopened, international travel resuming and far less masking this fall, flu is likely to make a comeback. (AP Photo/LM Otero, File)

ATLANTA — Doctors warn that this flu season could be particularly severe, renewing fears of a potential "twindemic" in which the spread of that virus and COVID-19 collide.

The last flu season was extremely subdued as concerns about COVID-19 prompted people to isolate, wash their hands frequently, avoid crowds and wear masks. There were no flu-related deaths in Georgia and only a few dozen flu-related hospitalizations in metro Atlanta, according to the state Department of Public Health.

Tennessee's flu activity was also minimal during the past season, with no influenza- related deaths reported in children or pregnant women since spring 2020, according to data from the Tennessee Department of Health.

But this flu season across the United States could be entirely different.

The unusually mild 2020-2021 season likely means natural immunity among Americans is waning, the Centers for Disease Control and Prevention said. In addition, pandemic safety measures have been relaxed.

Many adults have returned to the office, and children are back in school. People are once again gathering in crowded places such as football stadiums and concert halls. At the same time, fewer people are wearing masks and maintaining social distance.

That has doctors worried that fall and winter could bring a crush of flu patients filing into hospitals at a time when facilities are running low on beds. The highly contagious Delta variant led to a surge in cases that overwhelmed emergency rooms and intensive care units. Only in the past two weeks has the deluge has started to ease up.

Just 45 percent of Georgia residents are fully vaccinated against COVID-19.

In Georgia, the flu season usually starts in October and peaks between December and February. It typically ends in early spring, but it can stretch into May. Public health experts are urging people to get a flu vaccine as soon as possible.

"This year, we have different variables," said Dr. Cecil Bennett, a Newnan-based family physician.

With the hospital system already stretched so thin, a severe flu season would make it difficult for doctors to provide care to all patients.

"My concern is individuals who need to be hospitalized may be turned away and just given antibiotics when they need to be cared for in a hospital. They are triaging patients who, in normal circumstances, would be in the hospital. There is no place to put them."

The flu and the coronavirus have similar symptoms — including fever, cough and fatigue — so it can be difficult to tell the difference.

COVID-19 is more contagious and spreads more quickly than the flu, according to the CDC. Severe illness is more common with COVID-19. The mortality rate also is higher.

So far, more than 42.5 million people have had COVID-19 in the U.S., according to the CDC. More than 680,000 people in this country have died from it.

By comparison, during the 2019-2020 flu season in the U.S., about 38 million people contracted the illness and about 22,000 people died from it, according to the CDC. During that same season in Georgia, 94 people died of the flu, while more than 2,500 were hospitalized.

Getting a flu shot?

To maintain immunity throughout the flu season, September and October are the best months to get a flu shot, though getting the shot later is better than not at all.

Keep in mind that it takes about two weeks following the shot for antibodies that provide immunity to develop.

The CDC says it's OK to get a flu vaccine at the same time as a COVID-19 vaccine dose, including booster shots.

Even if a flu vaccine does not offer complete protection against contracting the flu, those who get the shots tend to have fewer days of symptoms, less severe symptoms and are less likely to need medical care.

Source: U.S. Centers for Disease Control and Prevention

Experts stress that influenza should not be taken lightly, especially cases in the elderly and young children.

"Every year in our hospital and other hospitals, when we have active flu seasons, we see many, many children hospitalized and unfortunately some who die," said Dr. Andi Shane, division chief of pediatric infectious disease at Children's Healthcare of Atlanta.

While the flu season is always unpredictable, North Carolina State University professor Julie Swann expects this season to be less severe than many in the past have been. It's true that fewer people than last year are masking up and taking other pandemic precautions, but many still are, said Swann, a health systems expert who served as a senior adviser to the CDC on the national distribution for the H1N1 flu vaccine.

Those precautions will help ease the severity of this flu season throughout the country, she believes. However, some places might be worse than others, depending on how well people are adhering to those guidelines for avoiding coronavirus infection and whether they get vaccinated against the flu, she said.

"This is all behavior-driven," she said.

Bennett said his patients tend to get both COVID-19 and flu vaccinations or neither.

The supply of flu vaccines doesn't appear to be an issue this year. Vaccine manufacturers are projecting there will be as many as 200 million doses available in the U.S., more than any other year in the past.

Earlier in the pandemic, when the COVID-19 vaccine was new, the CDC advised that people leave at least two weeks between that shot and other vaccines.

The agency now says it's OK to get a flu and COVID-19 vaccines at the same time.

The agency said it withdrew its earlier advice because it has more information on vaccine combinations.

Even so, some doctors, including Bennett, are administering the vaccines a couple of weeks apart. Bennett said giving the vaccines separately will help him track potential side effects from each vaccine.

Swann said she also likes the idea of getting the vaccines at different times, but only if a person can be "absolutely sure" they can get both vaccines.

Every year, there's a concerted campaign to coax people into taking the flu vaccine, with mixed success. About half of the U.S. population gets inoculated and, generally, 5 percent to 20 percent contract the flu.

The shot is usually effective in preventing flu infection in 40 percent to 60 percent of the people who take the vaccine, depending on how good a match it is to circulating strains. But experts stress that, even if a person gets inoculated and contracts the flu, the vaccine can lessen the severity of the illness.

Staff writer Elizabeth Fite contributed to this story.