Flu cases and deaths from the 2020–2021 season were drastically lower than usual—and that could spell trouble for this year's flu season.

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Flu season in the US, which runs from October through May, normally claims tens of thousands of lives every year. But there's never an exact number of flu deaths for any year—that's because the flu is not a reportable disease in most states, and not everyone who develops the flu seeks care or gets tested, according to the US Centers for Disease Control and Prevention (CDC). Instead, the agency develops estimates based on rates of laboratory-confirmed, flu-associated hospitalizations.

how-many-people-die-flu , Portrait of young woman wearing patient cloths sneezing in tissue at hospital. - Conceptual of sickness woman feeling when admitted in the hospital.
Credit: Getty Images

Last year, however, as the COVID-19 pandemic dominated the US, influenza cases were at an all-time low: Data from the CDC, supplied to JAMA, shows that out of 1.3 million specimens collected by labs between October 3, 2020 and July 24, 2021, only 2,136 were positive for influenza. Of those 2,136 influenza cases, there were only 748 flu-related deaths.

That's a huge difference from the rates of the 2019–2020 flu season. Per the CDC, there were an estimated 35 million flu-related illnesses—that number includes 16 million medical visit for the flu; 380,000 flu-related hospitalizations; and 20,000 deaths due to influenza.

Of course, those data are only from two specific years—and they show two very different ways the flu impacted the US population. Here's what you need to know about how many people die from the flu each year, on average, what infectious disease experts are expecting for the upcoming 2021–2022 flu season, and how to protect yourself.

How many people die of the flu each year, on average?

According to data collected by the CDC from 2010 to 2020, the agency estimates that the flu has caused 12,000–52,000 deaths annually. During that time, the flu also caused 9 million–41 million illnesses, and 140,000–710,000 hospitalizations. Globally, the World Health Organization (WHO) estimates that the flu kills 290,000 to 650,000 people per year.  

Those numbers can vary so much from year to year, because what we know as "the flu" isn't one specific thing—it's actually made up of different influenza strains that circulate. "How many people die of the flu each year of the flu is definitely related to the strains that are circulating, how accurately researchers were able to predict what should go into the flu vaccine, and how many people are vaccinated," Anjali Mahoney, MD, MPH, family medicine specialist with Keck Medicine of USC, tells Health.

Certain influenza strains can also be more severe than others. "Sometimes there are years where there are big genetic shifts, and we can see a very different virus," Cassandra Pierre, MD, MPH, an infectious disease physician at Boston Medical Center, tells Health. Robert L. Murphy, MD, a professor of infectious diseases at Northwestern Medicine Feinberg School of Medicine, agrees, saying that the flu virus is always changing. "[Sometimes] it can be a nastier strain," he tells Health. "It goes up and down."

How severe will the upcoming 2021-2022 flu season be?

It's far too soon to say, but experts are still worried about what could happen. "We're mildly terrified about how things could unfold with flu season this year," James H. Conway, MD, FAAP, a pediatric infectious disease specialist and associate director for health sciences at the Global Health Institute of UW-Madison, tells Health.

This is for a few reasons. First: Australia—which has its winter and flu season during summertime in the US—didn't have a flu season this year. While that could be good news for a less severe season in the US, it also spells trouble for vaccine formulation. "Usually when the powers that be are trying to figure out which strains to put in the vaccine, they are basing it on what circulated in the southern hemisphere during summer," says Dr. Conway. "They didn't have any flu season, so the powers that be couldn't figure out prevalent flu strains."

The low numbers of flu cases last year could also negatively impact this year's flu season. With lower-than-usual rates of both flu vaccinations and flu cases, the US population is "relatively immunologically naive," says Dr. Conway—that means we don't have any leftover immunity from last flu season. Pair that with more people going out into public more often with lessening mask restrictions, and it could lead to a potentially more severe flu season than last year.

How can you protect yourself from the flu?

The straightforward answer here: Get vaccinated ASAP. "The only protection people can get is getting vaccinated and being careful about respiratory viruses," says Dr. Conway.

The CDC recommends that everyone 6 months and older get a flu vaccine every year. It's the first and most important step that people can take to guard against the flu and its complications. The flu can be harder to fight off for specific populations, such as infants and young children, the elderly, and people who are immunocompromised due to chronic illnesses such as HIV or cancer—so it's especially for those populations to get vaccinated, possibly with a high-dose flu shot, if approved by their doctor.

Those recommendations put in place for protection against COVID-19 can also come in handy when preventing the flu virus. "Everybody masking during winter months could help a lot with preventing flu deaths," says Dr. Conway. "That's done pretty regularly in some areas of the world. That may be as much a part of our major protection as major vaccines." In addition to that, Dr. Conway suggests that people remain vigilant about staying home from work and school when they're ill. Proper handwashing and disinfecting surfaces can help keep illnesses at bay, as well.

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