Every year, millions of people in the United States get the flu. You can get the flu at any time of year, but most cases happen during flu season.

The exact dates of flu season change every year, but it typically starts when temperatures drop in the fall and ends when they rise in the spring. In the Northern Hemisphere, this generally means flu season runs from October through April.

Flu season in the United States runs from mid-fall to late spring, because the flu virus is more active and spreads faster when temperatures are chilly. The exact months change a little each year.

The Centers for Disease Control and Prevention (CDC) monitors flu cases yearly. When cases begin to spike in the fall, the CDC declares the start of flu season. During most flu seasons, the highest numbers of flu cases are reported between December and February, when temperatures are the lowest and the air is dry.

Although the flu virus can spread at any time, cases spike when temperatures and humidity levels drop. That’s why flu seasons worldwide are associated with colder temperatures.

While temperatures in Canada and most of Europe generally decrease at about the same time of year as those in the United States, this isn’t the case everywhere. For example, in countries in the Southern Hemisphere, such as Australia, Thailand, and South Africa, flu season generally runs from April through October or November.

As they do in the United States, the exact dates of flu seasons around the world change each year.

You might think of the flu as a mild condition. People often say that a cough or sneeze is “just the flu.”

But the flu can be very serious. People in high risk groups can experience severe flu symptoms that may lead to hospitalization and even death. High risk groups include:

  • young children
  • pregnant people
  • people 65 years old and older
  • people with asthma
  • people with heart disease
  • people with diabetes
  • people with conditions that affect the immune system

The flu spreads from person to person in respiratory droplets. Even if you have a mild case, you can pass the flu virus to others, including those in high risk groups.

Getting a flu vaccine is the best way to prevent the flu and avoid spreading the virus to others. Research has shown that flu vaccines reduce the risk of illness, hospitalization, and death.

When you think of the flu, you probably think of a single condition. But multiple strains of the influenza virus can lead to the flu.

Each year, researchers determine which strains of flu-causing viruses are likely to be the most common during the upcoming flu season. That research is used to create the flu vaccine for that season. That’s one reason it’s so important to get a flu vaccine every year.

Flu viruses change all the time, so last year’s vaccine might not protect against this year’s viruses. Plus, your immune system’s defenses from the flu vaccine fade with time, so getting vaccinated every year is a great way to stay protected. The vaccine is available as an injection or as a nasal spray.

People might assume that only those who are 65 years old or older or have weakened immune systems need to get the flu vaccine, but that’s not the case. The CDC recommends that everyone over 6 months old get a flu vaccine every year, including children and healthy young adults.

Young children are one of the groups at high risk for flu complications, so an annual vaccine is especially important for them.

There are some similarities between the flu and COVID-19. They’re both caused by viruses, both involve respiratory symptoms, and both tend to spike when temperatures drop. But different viruses cause these two conditions.

A flu vaccine won’t prevent COVID-19, and getting a COVID-19 vaccination doesn’t mean you won’t need a flu shot this year. Therefore, it’s important to get both vaccines. Plus, by reducing your risk for hospitalization from the flu, you’re reducing the demand on hospitals during the seasons when more people may contract respiratory viruses.

It’s nearly always a good idea to get a flu vaccine, but some people should not, including:

  • infants younger than 6 months old
  • people who have severe and life threatening allergies to some vaccine ingredients, such as gelatin or certain antibiotics

Other people need to talk with a doctor to make sure the flu vaccine is safe for them. This includes those who:

  • are currently feeling sick
  • have previously had a severe allergic reaction to a flu vaccine
  • have had Guillain-Barré syndrome in the past
  • have a mild allergy to gelatin, certain antibiotics, or any other common flu vaccine ingredient

Although some flu vaccines contain egg proteins, the CDC recommends that people with an egg allergy get vaccinated every year. The agency also states that no extra safety measures are necessary for this population.

In general, the CDC recommends that people receive all vaccines in a setting where healthcare professionals can monitor for an allergic reaction and treat it quickly if needed.

How to find a flu vaccine

Flu vaccines are available in a wide variety of places each year, such as:

  • pharmacies
  • health clinics
  • doctors’ offices
  • health centers
  • local health departments
  • workplaces
  • schools

You can find flu vaccines near you using the CDC vaccine finder.

The flu is caused by a contagious virus that mainly spreads when people who have the flu cough, sneeze, or talk near others. The virus can also spread through contact with surfaces that have been exposed to the virus. For example, if you have the flu and share a straw with someone, the virus could spread to the straw and then enter that person’s body.

The virus is contagious for a few days before symptoms start to show. This means the virus can spread to others before you even know you have it.

Flu symptoms include:

  • fever
  • sore throat
  • cough
  • aches and pain
  • nasal congestion
  • headaches
  • fatigue

Children with the flu might also experience:

  • nausea
  • vomiting
  • diarrhea

Because the flu shares symptoms with many other conditions, it’s not possible to find out whether you have the flu just by examining your symptoms. You’ll need to have a flu test to find out whether the flu is causing your symptoms.

A flu test requires swabbing the inside of your nose or the back of your throat to collect a sample that is then tested for influenza viruses. Multiple types of flu tests are available. Some will show results in as little as 10 minutes, while others take a few hours to deliver results.

Often, the flu clears up on its own with rest and over-the-counter treatment of symptoms. However, prescription treatment is sometimes necessary, especially for people in high risk groups.

Antiviral medications can shorten the duration of the flu and prevent you from developing serious complications such as pneumonia. Just like the vaccine, the recommended antiviral medications for the flu might change each flu season based on the specific virus strains that are circulating.

Flu season starts in the fall when the weather gets colder and flu cases start to spike. It generally ends in late spring.

For some people, the flu is a minor condition that is treatable at home. But for others, the flu can cause severe complications that may lead to hospitalization and death.

The best way to protect yourself and the people around you is to get the flu vaccine each year before the peak of flu season.