Flu killed and hospitalized more people in the United States last winter than any seasonal influenza in decades, according to new data released Thursday. It’s the most detailed picture of the devastating reach of the respiratory virus, which sickened millions of people as overwhelmed hospitals pitched tents to treat patients.

A nurse administers a flu shot, manufactured by Sanofi Pasteur, at Perry Memorial Hospital in Princeton, Illinois. (Daniel Acker/Bloomberg)

As a new flu season gets underway, public health officials say last year’s toll underscores the importance of getting a flu vaccine each year. The shot can prevent infections and reduce the severity of complications from the disease.

Influenza killed about 80,000 people in the 2017-2018 season, according to figures released by the Centers for Disease Control and Prevention. The previous high for a regular flu season, based on analyses dating back more than three decades, was 56,000 deaths.

“Last year was just a horrible season,” said Daniel Jernigan, head of the CDC’s influenza division. “It was just a tremendous amount of disease.”

There were record-breaking levels of illness, hospitalization rates and deaths in children. Pediatric deaths totaled 180, he said. Only the 2009 swine flu pandemic, which killed 358 children, was worse since health authorities began tracking child deaths from flu 14 years ago.

The CDC recommends that those 6 months and older get a flu vaccine before the end of October. It takes about two weeks for the body to produce a full immune response.

Despite the dreadful season last year, overall vaccination coverage remained flat; as in previous years, less than half of the U.S. population was vaccinated. But most concerning to officials was the drop in coverage among the youngest children – those under 5 – who are at highest risk for serious flu complications.

Officials and clinicians say they don’t know why more people did not get vaccinated given that last year’s flu season, which started early, dominated news during the winter and into March, and lasted for 19 weeks, making it one of the longest in recent years.

They speculate that some people decided that flu vaccines, which are never as effective as most other vaccines even in a good year, aren’t worth the effort. A new vaccine must be designed every year to best match influenza viruses circulating in the previous season. A preliminary estimate showing last season’s vaccine to be about 36 percent effective overall may have convinced some people not to bother, clinicians said. A final estimate shows the vaccine was about 40 percent effective in reducing a person’s risk of becoming sick enough to need to see a doctor.

But experts say focusing only on that measure misses too many other benefits of the vaccine that are less well-known. Flu’s impact on the body goes well beyond the acute respiratory infection, and a flu shot can prevent or reduce the severity of numerous complications.

“We’ve got to try to do something about the messaging,” said William Schaffner, medical director of the National Foundation for Infectious Diseases and an infectious diseases professor at Vanderbilt University.

The vaccine can reduce flu illness and hospitalizations, can protect pregnant women during and after pregnancy and be lifesaving in children, Jernigan said.

For older people with chronic health conditions, getting a flu shot is as effective at preventing a heart attack as quitting smoking, taking cholesterol-lowering drugs or taking blood pressure medications, recent studies show.

For those who are frail, a bout of flu can lead to losing independence in everyday activities, said Janet McElhaney, a Canadian geriatrician and researcher.

“Basically, this is a vaccine that can do other things,” said the CDC’s Jernigan. “We may not have been making as much of a push for that in the past.”

Pediatricians such as Wendy Sue Swanson, at Seattle Children’s Hospital, say that even an imperfect vaccine offers a layer of protection. It was about 67 percent effective against one of the influenza strains last year, meaning that of 100 kids lined up in a gym, if all of them got a flu shot, 67 of them wouldn’t get the flu if a sick child coughed on them. “That layer of added protection is important,” she said.

This year is the 100th anniversary of the worst pandemic in human history, the Spanish flu that killed 50 million to 100 million people during the winter of 1918-1919.

It’s virtually impossible to predict the coming flu season. The season in the Southern Hemisphere has been relatively mild, a possible indicator for what to expect in the United States.

The CDC uses mathematical modeling to estimate total flu-related deaths. Because flu seasons vary in length and severity, the estimates have ranged from a low of 12,000 deaths (during 2011-2012) to a previous high of 56,000 (during 2012-2013).

Last season, more than 900,000 were hospitalized, double the number during many regular seasons.

Among the child deaths reported to CDC last season, about 80 percent were in children who were not vaccinated. More than one-third occurred among children between 6 months and 4 years. Flu vaccination coverage for that group was 67.8 percent, which was lower than the 70 percent reported in the previous season, and about the same as it was five seasons earlier.

Swanson, who heads digital innovation at Seattle Children’s Hospital, recently created a new skill for Amazon.com’s voice-assistant device, Alexa, called Flu Doctor to answer questions about flu. (Jeff Bezos, the founder and chief executive of Amazon, owns The Washington Post.)

“I’m just trying to figure out how to build trust,” she said. “In the end, fear tactics aren’t that effective. Parents feel a responsibility to their own child. They’re mostly motivated to keep their kid alive.”