The crushing coronavirus pandemic is fueling record numbers of infections and hospitalizations even as the nation hurtles toward the peak of flu season, triggering an urgent call for flu vaccinations.

The flu season so far appears mild, but health experts remain concerned and warn that if a feared "twindemic" of COVID-19 and the flu materializes, it could overwhelm hospitals and further strain health care professionals already stretched thin in their battle against COVID-19.

"It is definitely not too late for a flu shot," said Dr. Edgar Herrera Sanchez, vice chairman of the Orlando Health Infectious Disease Group in Florida. "Everyone should be getting a flu shot each year, and especially this year."

The exact timing and duration of flu seasons can vary, but flu cases often begin their rise as early as October. Activity peaks between December and February and can last as late as May. Flu inoculation usually kicks in about two weeks after receiving the shot and lasts about six months.

Nationwide, flu-related health care visits last week were only about half the normal rate for early November, the Centers for Disease Control and Prevention reported. But the CDC noted that the COVID-19 pandemic has altered patterns when Americans seek medical aid. And it is still early in the season.

Sanchez says influenza and COVID-19 are respiratory viruses and thus share "routes of transmission." Masking, hand-washing and social distancing, relentlessly preached by public health experts to help suppress the coronavirus, are also effective against influenza – and possibly more so since COVID-19 is much more contagious, he said.

Ogbonnaya Omenka, an associate professor and public health specialist at Butler University, says those measures, plus isolating sick people and "more deliberate protection of the more vulnerable members of the population" such as elderly people and those with diabetes, obesity, or other high-risk conditions, could result in a more contained flu season.

"Still, influenza kills up to 60,000 patients a year so we know this can be deadly," Sanchez said. "The last thing we need is another virus that is vaccine-preventable to add to the total number of hospitalizations."

Dr. Alex Kemper, chief of primary care pediatrics at Nationwide Children’s Hospital in Columbus, Ohio, said flu shots are crucial because mask-wearing and other prevention strategies are "unfortunately variable across communities in the United States."

Even President-elect Joe Biden, an ardent supporter of masks unlike President Donald Trump, has said he won't be able to issue a nationwide mask mandate. He says he is hoping for cooperation from governors and mayors.

While some state leaders such as New York Gov. Andrew Cuomo urge or mandate residents to wear masks, others including South Dakota Gov. Kristi Noem show little interest. Last week, as her state's COVID-19 numbers soared, Noem posted photos on Twitter of herself with elderly, and thus vulnerable, Aberdeen businesspeople. No masks, no social distancing.

"Those who don’t want to wear a mask shouldn’t be shamed into it, and government should not mandate it. We need to respect each other's decisions," she in a Twitter post last month, adding that "in South Dakota, we know a little common courtesy can go a long way."

Countries in the southern hemisphere such as Australia or Chile, who "flip-flop" their flu season with ours, have had relatively few cases of influenza, public health experts say. But Kemper stressed that the flu shots that protect individuals from getting sick also help keep clinics, emergency departments and hospitals from further overwhelmed amid the pandemic.

In North Dakota, Gov. Doug Burgum decreed that health care professionals who test positive but are asymptomatic can continue to work because hospital staffing is so thin. In Wisconsin, there were just 128 intensive care beds available Tuesday – a supply that experts said could evaporate next week if current trends continue.

"Wisconsin, this is serious. This crisis is urgent," Gov. Tony Evers warned. "It's not safe to go out, it’s not safe to have others over – it's just not safe. And it might not be safe for a while yet."

Melissa Nolan, an infectious disease expert and professor at the University of South Carolina, warned that the Southern Hemisphere flu seasons revealed that "co-infections" of COVID-19 and flu are more likely to result in severe illness than infections of one or the other.

"We are hopeful that the United States will also experience a mild influenza season," she said. "But we still recommend everyone get their flu shot."