Learn the best time to get your flu shot—and 5 other important facts

Flu season typically begins in October and lasts until May, though most illnesses usually occur between December and February. Each season, tens of millions of people get the flu. During the 2024-2025 flu season, there were at least 43 million confirmed flu cases, according to end of year estimates from the Centers for Disease Control and Prevention (CDC). Despite those high numbers, there remain a lot of myths and misunderstandings surrounding the flu virus. 

Here are the facts about the flu, so you can stay healthy this season. 

There are only two types of the influenza virus—types A and B—that can cause the seasonal flu. But many people believe the flu can be caused by exposure to weather, bacteria and other factors, says Sarah Park, MD, FAAP, a pediatric infectious disease specialist in Honolulu.  

“I’ve heard people call a stomachache the ‘stomach flu,’ or they have a cold and they’re calling it the flu. Only the flu virus can cause the flu. It’s pretty distinct," Dr. Park says. 

Because they share symptoms, it can be hard to tell the difference between a common cold and the flu. Generally, cold symptoms are milder. Having a fever, chills, and muscle or body aches often indicates the flu. Contact a healthcare provider if you have these symptoms and are: 

• Pregnant 
• Older than 65 
• Have a chronic illness 
• Have a weakened immune system  

It’s important for these high-risk groups to seek medical care to avoid potential complications. 

Though eating a healthy diet, exercising, and getting plenty of sleep are key to well-being, they won’t necessarily protect you from catching the flu. No type of person is more or less likely to get the flu virus, but some people are more likely to contract a more severe infection than others. “People with underlying respiratory conditions, like asthma, can have more complications related to the flu or have a prolonged bout of the flu,” says Dr. Park. 

People who are healthy, overall, can generally bounce back after contracting the flu. But those with underlying conditions, or people in higher-risk groups, such as pregnant people, older people or those living with chronic illnesses, may require hospitalization, antiviral medications or additional treatments. 

There are two ways to be immunized against the flu. The first is a shot. The second is a mist that is sprayed into the nose. People can get a flu shot from their healthcare provider (HCP), at a local pharmacy, or at an urgent care center. Some community health clinics offer flu shots. And some employers provide on-site flu shots for their employees. Most insurance companies cover the cost of flu shots. So, getting one may come at no additional cost to you. 

On September 20, 2024, the Food and Drug Administration (FDA) approved the nasal spray flu vaccine, FluMist, for self- or caregiver administration. This means you can give it to yourself or someone else at home. FluMist is approved for people between the ages of 2 and 49. So those who are younger than 2 or older than 49 are not eligible to receive it. Some groups also shouldn’t receive the FluMist, including pregnant people and those with certain health issues. Ask a healthcare provider (HCP) what is best for you. 

The flu shot can cause side effects like soreness and swelling at the site of injection, headache, and nausea, but it cannot cause the flu. Vaccines contain inactivated virus—so they’re no longer infectious—or components that look like the flu virus, so your immune system is ready when it encounters the real thing. FluMist contains a live but weakened virus that cannot cause illness. 

 “[The flu vaccine] should not make you sick because the protein in it cannot make you sick. It’s more likely that you were infected waiting in line at the doctor’s office or pharmacy. It takes two weeks before immunity [from the vaccine] is fully developed, so if you’re exposed to someone contaminated in that time, you’re going to get sick," Dr. Park says. 

Getting a flu shot is the best way to protect yourself from the flu. The next best thing you can do to avoid the flu—and many other diseases—is to wash your hands well and often, says Park.  

Remember: Lather up and scrub the fronts and backs of your hands, between your fingers, and under your fingernails for at least 20 seconds (or about the time it takes to sing “Happy Birthday”). If you don’t have access to soap and water, use hand sanitizer that contains at least 60 percent alcohol. You can also help prevent flu transmission by avoiding close contact with people who have the flu and avoiding touching your eyes, nose, and mouth. 

If you already have the flu, stay home to protect those around you in your community. You can help prevent spreading the virus by keeping yourself away from others.  

Since the flu vaccine contains trace amounts of egg proteins, it used to be recommended that people with egg allergies not be vaccinated or be monitored for signs of an allergic reaction for up to 30 minutes after receiving the vaccine. 

In 2016, however, the Advisory Committee on Immunization Practices (ACIP) updated its guidelines for people with egg allergies.  

• There’s no longer a 30-minute monitoring period for those who have experienced mild allergic reactions, such as only hives, after a flu shot 

• Those who have had serious allergic reactions after a flu shot, such as swelling or difficulty breathing, should receive their vaccine in a doctor’s office equipped to manage severe allergic responses 

• Those who have had severe allergic reactions after a flu shot shouldn’t be vaccinated 

Be sure to talk to your doctor or pharmacist about any previous allergic reactions you’ve had to the flu shot, including side effects (like hives or difficulty breathing) and the duration of your reaction. 

When is the best time to receive your flu vaccine? It is possible to catch the flu at any time of the year, but it is best to be vaccinated early in the flu season, which generally starts in October.  

It can take up to two weeks for full immunity to develop after being vaccinated. So, try to visit your pharmacy or healthcare provider to get your flu shot sometime in October.