The 9 Worst Flu Shot Mistakes According to Immunity Experts—Plus, Here’s Who Needs a Flu Shot in 2025

How bad will the 2025-2026 flu season be? 

The exact timing, duration and severity of flu seasons vary each year and can only really be understood in retrospect, explains Robert Amler, MD, MMS, MBA, FAAP, FACPM, dean of the School of Health Sciences and Practice at the Institute of Public Health at New York Medical College. The ongoing circulation of new COVID strains and RSV (respiratory syncytial virus) complicate predictions further, as these illnesses have similar symptoms and are difficult to distinguish clinically. 

Still, while predictions aren’t an exact science, they do tend to offer reliable estimates to help health authorities and the public prepare for virus season, says Linda Yancey, MD, a board-certified infectious disease physician at Memorial Hermann Katy Hospital in Texas.

Dr. Yancey explains that every year in March, the U.S. Food and Drug Administration (FDA) reviews data from the previous flu season and which strains are circulating in the Southern Hemisphere during their winter. This data explains what flu season will look like in America.

For instance, four dominant flu strains have been in circulation during the past decade. But by tracking patterns and reviewing data, the FDA is now advising vaccine manufacturers to focus on just three flu strains for the 2025-26 season: Influenza A (H1NI), an A (H3N2) virus, and a B/Victoria virus.

This year, flu season began earlier than usual in Australia—just as it did in 2023 and 2024—and experts say that pattern could signal a longer and more intense season ahead. Australia is already seeing its worst flu year on record, and historically, America’s flu trends often mirror those seen there.

Still, no matter the severity of this year’s flu season, the best way to protect yourself and your loved ones is to get your flu shot—yes, you: “Simply put, because it works,” Dr. Yancey says. “The flu shot is recommended for everyone. It doesn’t prevent all flu cases, but it dramatically decreases the odds of getting a severe case.” 

She adds that you should get the 2025 COVID-19 shot while you’re at it since most people can get both the flu shot and COVID shot on the same day.

For the 2025–2026 season, the American Academy of Family Physicians (AAFP) recommends annual COVID-19 vaccination for all adults 19 and older, as well as vaccination for children ages 6–23 months. For kids and teens ages 2 to 18, the AAFP supports a risk-based single-dose approach and encourages families who wish to be vaccinated to do so. The organization also recommends COVID-19 vaccination during any trimester of pregnancy and while breastfeeding—guidelines consistent with those of the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists.

When should you get your 2025-2026 flu vaccine?

With a potentially earlier start to the flu season and multiple viruses circulating, it’s a good idea to get your flu shot as soon as possible, Dr. Yancey says. “Vaccines work best if they are given prior to exposure to the disease,” she explains. “Getting a flu shot early in the season ensures that your immune system will have time to build immunity.” This means most folks should get the flu shot in September or early October, although it can still help if you get it later.

However, if you’re over the age of 65, you should talk to your doctor about when to get your flu vaccine, as well as about getting one of the higher-dose vaccines, according to Hareesh Singam, MD, an infectious disease specialist at Cleveland Clinic. In the past, experts have advised waiting until at least late October to get vaccinated because the protection wanes more quickly in older individuals. This means if you’re older and get the vaccine too soon, protection might not last the entire flu season. Still, talk to your doctor for personalized recommendations. 

Why you should get your flu shot

Many people underestimate influenza, but this seasonal virus causes millions of cases and thousands of deaths each year. According to the U.S. Centers for Disease Control and Prevention (CDC), between October 2024 and May 2025, an estimated 47 million to 82 million Americans contracted influenza. The CDC classified it as a high-severity season across all age groups—the first since 2017–2018. 

While experts expect this year’s flu season to be somewhat milder than last year’s, vaccination remains essential. The CDC notes that the annual flu shot lowers the likelihood of a doctor visit for flu by 40% to 60%. (Though many vaccines offer near-total protection against contracting a disease, the flu shot isn’t one of them.)

But if that seems like a safe margin to gamble with, you might want to think again. The flu is a serious illness that can lead to pneumonia, hospitalizations and death, says Margaret Khoury, MD, a pediatric infectious disease specialist at Kaiser Permanente’s Baldwin Park Medical Center. The flu vaccine not only lowers your risk of catching the flu but reduces the chance you’ll develop serious complications.

The CDC spells it out like this: during the 2023–2024 season, flu vaccination prevented an estimated 9.8 million flu-related illnesses, 4.8 million medical visits, 120,000 hospitalizations, and 7,900 deaths. The vaccine is especially critical for children—the CDC reports that 89% of kids who died from influenza last year were unvaccinated.

While the only real way to mess up your flu shot is not to get it at all, top experts explain below the biggest mistakes people make regarding the flu vaccine.

Flu shot mistake #1: Not getting the vaccine because you think you’re too old—or young

Anyone older than six months should get the flu vaccine (unless you have a medical reason to avoid it, such as an allergy or an immune disorder), Dr. Khoury says, adding that this is especially important for the following groups:

• Children older than six months or anyone who cares for children
• The elderly or their caregivers
• Pregnant women
• People with asthma, heart disease, or diabetes
• Anyone over age 50
• Anyone who suffers from an autoimmune disease
• Anyone who lives in a nursing home or long-term care facility
• Those with obesity
• All healthcare workers

Flu shot mistake #2: Skipping this year’s flu shot because you got one last year

Every year, influenza viruses mutate, which means the virus isn’t the same as the one you were vaccinated against last year. “People need to get the flu shot every year because flu viruses are constantly changing, and it is not unusual for new flu viruses to appear each year,” says Caroline Sullivan, DNP, ANP-BC, a nurse practitioner and primary care provider at Spring Primary Care and Wellness in New York City. Plus, Sullivan says, “Studies have shown that the body’s immunity to influenza, either through natural infection or vaccination, declines over time.”

As we referenced above, here’s how each year’s flu vaccine works: Ahead of each flu season, health experts worldwide determine which flu strains pose the greatest threat. This research informs what goes into that year’s flu shot—exactly how effective it is depends on the accuracy of those predictions, with some years faring better than others. 

The final product is either a “trivalent” or “quadrivalent” flu shot, which means it protects against the three or four strains of influenza in circulation. (And FYI, this year’s flu shot is trivalent, as one prevalent strain of the flu disappeared during the pandemic thanks to COVID precautions.)  So, even if experts only get one or two strains correct, it’s still worthwhile to get the shot, Dr. Khoury explains.

If you got the vaccine last year and still came down with the flu, it’s natural to question getting the flu shot again. Still, experts say that in these scenarios, the virus had mutated—and the vaccine hadn’t kept up—or your illness was not actually influenza but another virus altogether. (Plus, if you are vaccinated and catch the flu, your illness could have been worse as the vaccine helps reduce the risk of flu-related hospitalization.)

Flu shot mistake #3: Avoiding the vaccine because you suspect you already got the flu

Are you sure it was the flu and not some other recent virus? Not only can you not be sure you’ve had it (unless you were tested), but multiple strains of influenza are circulating every year—so getting one strain doesn’t protect you from the others, Dr. Khoury says.

As a bonus, even if you are sick, the flu shot can lessen the severity of your illness and protect you from other viruses through cross-protection antibodies, she says. These viruses are similar to the flu strains in the flu vaccine, which your body learns to fight off.

Flu shot mistake #4: You believe the flu vaccine will actually give you the flu

Our experts say this is the most common misconception people have about the flu shot—but science doesn’t back it up. “This is biologically impossible,” says Ryan Maves, MD,  an infectious disease and critical care physician at Atrium Health Wake Forest Baptist. “No living virus is capable of causing human infection in any injectable influenza vaccine.”

Dr. Khoury explains the flu shot is made in such a way that it either contains no flu virus at all or an inactivated or noninfectious virus. So, while the flu vaccine may cause a low-grade fever and muscle aches in some people, these symptoms are usually temporary and are not actually an influenza infection.

Flu shot mistake #5: You make the flu vaccine hurt more than it should by tensing up

Fear of needles is a very common reason people avoid the flu shot, and there are ways to help you deal with this, says Amy Baxter, MD, a double board-certified pediatric emergency physician. “I do the scientific research on why, but the important thing is once someone is afraid, they tend to keep that fear for life,” she says.

Fortunately, you can have some control over how painful the vaccination experience is for you. “Tensing a muscle makes it hurt more, so try to relax the arm and focus on breathing,” says Baxter. “There are many strategies to reduce needle fear, but it usually takes three good experiences to help someone overcome it.”

Flu shot mistake #6: You don’t move your body immediately after your flu shot

A 2022 study published in the peer-reviewed scientific journal Brain, Behavior, and Immunity found that light to moderate exercise—like walking or jogging—30 minutes after you get your flu shot helps your body churn out more flu-fighting antibodies. (The study also shows that this is true for the COVID-19 vaccine—and that exercise doesn’t increase the vaccine’s side effects.)

Moreover, the enhanced immune response from just that one workout lasts for weeks beyond your vaccination. 

Flu shot mistake #7: You wait too long to get the vaccine

A typical flu season in North America starts as early as October and continues into May—and the flu shot works best early in the season, Dr. Khoury says. The sooner a person is vaccinated, the more antibodies and immunity they can develop before the height of flu season, which is January and February.

Since it takes about two weeks to build up immunity after receiving the vaccine, the CDC recommends getting the flu shot as soon as it is available (which is why most doctor’s offices and pharmacies start offering it as early as September).

But if you find yourself unvaccinated in late January or February, getting the flu vaccine is still recommended—better late than never.

Flu shot mistake #8: You don’t get the flu vaccine because you’re pregnant or breastfeeding

This is an understandable question among pregnant and breastfeeding women, as well as those trying to conceive, but from the CDC and our immunity experts, the verdict is in: You should absolutely get vaccinated. “Pregnant women should definitely get a flu vaccine, as they’re one of the most susceptible populations and can become seriously ill and even die from the flu,” says Laura Haynes, PhD, a professor in the Department of Immunology at the University of Connecticut. (If you’re pregnant, you should also know about this vaccine.)

Plus, if you’re breastfeeding an infant and have received the vaccine during your pregnancy, then you pass the immunity you acquired from the vaccine onto your newborn or infant. This is called “passive immunity”, and it’s a benefit of breastfeeding, she explains. 

The current CDC guidelines for pregnant women receiving a flu shot are as follows:

• Pregnant women in their third trimester can get a vaccine in July or August to protect their babies from the flu after birth.
• Pregnant women in their first or second trimester should wait until September or October to vaccinate unless directed by their doctor. 

Be aware that the FDA has approved an RSV vaccine for pregnant women for its passive immunity benefits. While RSV is fairly mild in adults under age 65, it can be incredibly dangerous for babies. So, this maternal dose offers vital protection for infants from birth. 

Flu shot mistake #9: You think the flu’s not that bad

Often, the flu can mimic a bad cold, with symptoms like a runny nose, a sore throat and a cough—and a mild case can minimize how dangerous the illness really is. However, the flu is more than just an inconvenience: The virus still kills tens of thousands of Americans annually.

Deaths from the flu generally occur due to complications such as pneumonia, secondary infections, or the worsening of existing medical conditions. In fact, CDC data show that during the 2023–2024 flu season, nearly 90% of adults hospitalized with influenza had at least one chronic health condition that increased their risk of severe complications.

Moreover, “the most common risk factor for severe influenza or COVID-19 is a risk factor that most of us will hopefully experience eventually, which is being over 65 years old,” Dr. Maves says. That’s why it’s so important to get the flu shot—not just to protect yourself—but to help ensure protection for those in your community in this high-risk category. 

For more wellness updates, subscribe to The Healthy @Reader’s Digest newsletter and follow The Healthy on Facebook and Instagram. Keep reading:

• The Red Cross Says Doing This Is Essential After Your Flu Shot & Covid Booster
• How Do Antibiotics Work? An Infectious Disease Doctor Explains
• Over 50? Getting This Vaccine Could Slash Your Heart Risk By 16%, Says New Study
• I Just Got the Pneumonia Vaccine, and I’m Only in my 30s—Here’s Why I Made the Decision

Additional writing and reporting by Charlotte Hilton Andersen.