What Doctors Want You to Know About Flu Vaccine Side Effects

WHEN FALL APPROACHES, you might be looking forward to cooler weather and football games. Nobody’s looking forward to flu season. But you can help protect yourself by getting a flu shot. If you’re hesitating because you’ve heard rumors about the vaccine, put your mind at ease with these facts.

The Centers for Disease Control and Prevention (CDC) recommends that everyone over six months old get vaccinated against the flu and that September and October are the ideal times to get the shot.

Flu season typically runs from mid-fall to mid-spring, says S. Wesley Long, M.D., associate professor of pathology and genomic medicine at Houston Methodist. “I tell people to get the flu shot early in the season, and you should have good coverage through the holiday season when people are going to congregate.”

But if you miss that window, don’t worry. Dr. Long says it’s never too late in the season to get vaccinated. Flu can happen year-round; it’s just less common in the summer.

The vaccine is formulated a little differently each year to work against current flu strains, Dr. Long says. “It helps make sure you’re covered against whatever is circulating.”

Flu shots can reduce the likelihood of severe illness, hospitalization, and death from the flu. The CDC estimates that there were 35 million to 65 million flu illnesses and 25,000 to 72,000 flu deaths last year.

“The flu vaccine is an important part of keeping yourself and your community safe, along with washing your hands, covering your nose and mouth when coughing or sneezing, and avoiding exposing other people when you are sick,” says Shivanjali Shankaran, M.D., an infectious disease physician and associate professor at RUSH Medical College in Chicago.

While it’s crucial to get a flu shot, the vaccine can come with some side effects—but side effects don’t mean that the shot gave you the flu. Think of them more as a way to know your immune system is working. Here’s what you should know about the side effects of the flu vaccine.

Common Flu Shot Side Effects

Flu shots are safe and generally well-tolerated by most people, Dr. Shankaran says.

Still, some people might experience a few side effects, including:

• Pain, redness, or swelling near the injection site
• Headaches
• Fever
• Nausea
• Sore muscles

“Most people have a little redness and soreness at the site of the inoculation,” says Andrew Pekosz, Ph.D., professor of molecular microbiology and immunology at the Johns Hopkins University Bloomberg School of Public Health. “These are normal symptoms and are due in part to your body’s immune system reacting to the vaccine.”

But most people have mild side effects, if any, adds Jay Lee, M.D., a member of the American Academy of Family Physicians board of directors and medical director of Integrated Health Partners of Southern California.

Does the flu shot give you the flu?

This is a myth, Dr. Long says. Flu vaccines don’t contain any live virus, just pieces of it that are made synthetically to help your immune system recognize the flu when it comes into contact with the real thing.

Getting the actual flu from the flu shot is “physiologically impossible,” he says. “It’s administered into your arm muscle, which is not a place the flu virus normally goes to. So there is no possibility you can get the flu from the flu shot,” Pekosz adds.

If you notice flu-like symptoms after getting the shot, it could be from a cold or another virus that’s floating around during flu season, Dr. Long says. Most people do get their flu shots at the height of respiratory illness season.

Flu Shot Side Effects You Should Worry About

Although extremely rare, it is possible to develop an allergic reaction to the flu shot. Typically, signs appear within a few minutes of receiving the vaccine and include:

• Trouble breathing
• Wheezing
• Swelling around eyes or mouth
• Hives
• Feeling weak
• Dizziness

If you’re eligible for inoculation via nasal spray (see the CDC’s list of people who shouldn’t get the nasal spray—including children younger than age 2 and people age 50 and older—here), side effects in adults can include a runny nose, headache, and cough.

Also, note if any symptoms that started out as mild seem to be getting worse, Dr. Lee says. If that happens, call your doctor.

What’s new with the 2024-25 flu vaccine?

There are many types of flu viruses—and each consistently changes. This means that the U.S. flu vaccines are reviewed every year to protect against the currently circulating flu viruses.

While the medical community won’t have the full picture of the latest vaccines until after flu season starts, the CDC has issued a few recommendations for the 2024-25 flu season.

This year’s vaccine will be trivalent, meaning it’s designed to protect against three different influenza viruses: H1N1, H3N2 and a B/Victoria lineage virus.

Vaccines have been quadrivalent in recent years, which means they offered protection against four viruses. The CDC says it’s moving to a trivalent this year since a virus that has been included hasn’t been detected since before March 2020.

Can you get the Covid, flu, and RSV vaccines at the same time?

The CDC says that Covid and flu vaccinations can be given at the same time.

“For the majority of people, they will need a flu and Covid vaccine,” Dr. Shankaran says. “You can get both on the same day, one in each arm.” But you don’t have to get them all at once (just be sure to get all of them).

If you’re someone who should get an RSV vaccine, you can also get that one at the same time as the flu and Covid shots, Dr. Shankaran says. (The RSV vaccine isn’t currently recommended for everyone. It’s recommended for some pregnant women, babies under eight months old, and people over 60.)

The Covid and flu vaccines are recommended for everyone over six months of age, according to the CDC.

Can you still get sick even if you get the shot?

“The flu vaccine protects against influenza virus, but there are a number of other viruses that can cause a flu-like disease,” Pekosz said.

For instance, viruses like human parainfluenza virus, RSV, and coronaviruses all circulate in fall and early winter. These viruses and their symptoms usually last two to eight days.

Even if you get a flu shot, it’s possible to develop the flu. But the vaccine usually means your illness won’t be as severe.

“The flu shot remains safe and effective at preventing severe flu that could result in hospitalization or worse, death,” Dr. Lee says.

The Bottom Line on Flu Shots and Side Effects

It’s normal to feel soreness, redness, tenderness, or even develop a mild fever or body aches a couple of days after you get vaccinated—that’s just your immune response, not the flu itself.

So there’s no reason to avoid getting the flu shot because you think it’ll make you sick. Unless you have severe or life-threatening allergies to the flu vaccine or any ingredients in it, most people should roll up their sleeves for one each year, the CDC says.

Getting sick with the flu can be dangerous. While most people recover, some can develop complications, such as sinus and ear infections, pneumonia, and inflammation of the heart (myocarditis), brain (encephalitis), or muscle (myositis, rhabdomyolysis). It can even be deadly.

Even people who are otherwise healthy can get the flu—and they can get very sick and possibly need to be hospitalized, Dr. Long says.

“The flu shot is just a very simple way to protect yourself from getting influenza but also to protect your friends, your family, your loved ones, your co-workers,” he says.