When Does Flu Season Start?

Published July 5th, 2022 by Chris Riley
Fact Checked by
Jacqueline Hensler
Medically Reviewed:
Erik Rivera

The flu virus is a highly contagious respiratory illness that can cause severe fever, body aches, and fatigue among many other symptoms.

It is caused by the influenza virus, which comes in several different strains that we will detail below.

Each year, the Centers for Disease Control and Prevention (CDC) monitors the spread of the flu and issues updates after it begins about when it peaks and how long it is expected to last.

In this article, we will answer all of your questions about flu season including when it is, how the data is collected and monitored, and what your treatment options are if you get the flu.

What is the flu?

The flu, also called influenza, is a viral infection caused by a group of three flu viruses that affect humans that can cause mild to severe illness.

The three influenza viruses are: influenza type A, influenza type B, and influenza type C. Influenza A viruses are the most common, can cause severe illness, and are the source of all flu pandemics.

Influenza B viruses typically cause less severe illness than influenza A viruses and are only found to cause epidemics.

Influenza C viruses rarely cause serious illness in humans.

The way these respiratory viruses are transmitted is usually through person-to-person contact via respiratory droplets, like saliva or mucus, when you are infected and cough, sneeze, talk, or sing.

The flu virus can also be transmitted by touching surfaces that have the virus on them and then touching your eyes, nose, or mouth.

The main difference between the flu and the common cold is that flu symptoms are generally more severe than cold symptoms.

What are the symptoms of the flu?

The flu has a rapid onset of symptoms, usually within a few hours, that come on suddenly.

The incubation period when you are infected but not showing symptoms of the flu is typically one to four days before the development of symptoms although you usually start to become sick within a day or two.

Common symptoms of the flu include:

  • Fever (usually 100°F or higher)
  • Chills
  • Dry cough
  • Sneezing
  • Congestion
  • Runny nose
  • Nasal congestion
  • Muscle aches or body aches
  • Headaches
  • Fatigue or tiredness
  • Sore throat

Children are also more likely to experience vomiting, nausea, and diarrhea although you can experience them as an adult too.

The duration of illness usually lasts for a week although if you are over the age of 65 or have a weakened immune system then the symptoms can last for longer and the same goes for children too.

You are most contagious the first three to four days after your symptoms develop due to the fact that this time period coincides with when you will be most likely to cough and sneeze more often.

If your fever subsides for 24 hours without the aid of fever-reducing medications then you are no longer contagious.

What are the complications of the flu?

If you are a healthy person, the flu will likely go away on its own after a week or so and you will recover without any complications.

However, you may develop serious complications as a result of the flu that can lead to hospitalization or even death in severe cases. These complications include:

  • Bacterial pneumonia
  • Bronchitis
  • Sinus infections
  • Ear infections
  • Dehydration
  • Brain inflammation (encephalitis)
  • Heart inflammation (myocarditis)
  • Kidney failure
  • Sepsis
  • Bloodstream infections (septicemia)
  • Reye's syndrome (in children and adolescents)

If you are pregnant you are also at a higher risk for complications from the flu as pregnant women who get the flu are more likely to be hospitalized and have a higher risk for serious illnesses like pneumonia or bronchitis that can lead to premature labor, low birth weight, or stillbirth.

Other chronic health conditions can also put you at a higher chance for complications from the flu and these include:

  • Cancer
  • Respiratory diseases or chronic lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis
  • Diabetes
  • Heart disease
  • Kidney disease
  • Liver disease
  • Neurological and neurodevelopmental conditions like cerebral palsy, epilepsy, and stroke
  • Weakened immune system due to HIV/AIDS or other immunosuppressive illnesses, medications, or treatments
  • People who are morbidly obese (BMI of 40 or higher)

Recognizing the symptoms early on and getting treated quickly is the best way to avoid any flu-related complications from developing.

If you think you might have the flu and are at risk of developing complications due to a medical condition, it is important to see your doctor as soon as possible so they can prescribe antiviral medication if necessary.

When does the flu season start in the United States?

Annual flu season usually starts in October and can last as late as May with peak flu activity typically occurring between December and February.

However, the timing and duration of flu season can vary from year to year.

How is the data for flu season collected and monitored?

The data for flu season is collected by the CDC through their Flu Surveillance Program.

The data is collected from sentinel providers, which are a group of outpatient medical providers who see and report on patients with influenza-like illness (which includes flu infections and flu-related hospitalizations), clinical laboratories, as well as state and local public health departments.

These weekly reports are then compiled into the Weekly U.S. Influenza Summary Update which is a weekly surveillance report used to track the spread of influenza infections and influenza-like illnesses across the United States.

There is usually a week-long gap in data as it takes the CDC a week to compile and analyze all the data.

What are the treatment options for the flu?

If you have the flu, there are a few different treatment options available.

If you are a healthy adult, you most likely will not have to see your doctor unless your symptoms are severe or you are at a higher risk for developing complications due to the flu.

The first line of defense if you do have to see your doctor is usually antiviral drugs. These prescription medications can help lessen your symptoms and make them go away faster while also helping you avoid hospitalization.

They can also help prevent serious flu complications, like bacterial pneumonia, sinus infections, ear infections, and organ failure. Antiviral drugs are most effective when taken within the first 48 hours of having flu symptoms.

There are four different antiviral drugs that are approved by the FDA for the treatment of the flu:

  • Oseltamivir (Tamiflu)
  • Zanamivir (Relenza)
  • Peramivir (Rapivab)
  • Baloxavir marboxil (Xofluza)

These antiviral medications are available by prescription only and only oseltamivir is available in generic form.

In addition to antiviral drugs, there are also other treatment options available for the flu. These include:

  • Getting plenty of rest
  • Drinking lots of fluids
  • Take over-the-counter medications such as ibuprofen or acetaminophen to help reduce your fever and over-the-counter cough suppressants if you have a cough
  • Using a humidifier or taking a hot shower to help with congestion
  • Avoiding alcohol and nicotine

If you have the flu, it is important that you stay home from work, school, or other public places until at least 24 hours after your fever has gone away without the use of fever-reducing medications to help prevent the spread of the flu to other people.

What are the best prevention methods for the flu?

The best way to prevent the flu is by getting a seasonal flu vaccine each year. Flu vaccinations are safe, effective, and available for anyone over six months of age.

There are several different types of flu vaccines including the normal vaccination shot, a vaccination shot that is made without using chicken eggs if you have an egg allergy, and a nasal spray flu vaccine.

All vaccines are quadrivalent vaccines, meaning they will help to prevent four different flu strains.

The annual flu vaccination has a slight risk for mild side effects such as a low-grade fever for a day or two or soreness.

It is important to get the annual flu vaccine as soon as it is available because the flu virus can mutate and change from season to season. There are also some other things you can do to help prevent the spread of the flu, such as:

  • Washing your hands often with soap and water or using an alcohol-based hand sanitizer
  • Avoiding close contact with an infected person or wearing a facemask if you have to be around them and practice social distancing
  • Avoiding touching your eyes, nose, and mouth
  • Covering your mouth and nose when you sneeze or cough with a tissue, sleeve, or the crook of your elbow (not your hands)
  • Cleaning and disinfecting surfaces that are often touched, like doorknobs, light switches, toys, and phones

In addition to the flu vaccine and taking preventive measures, it’s also important to know what to do if you or someone you know does get the flu.

Be sure to seek medical help right away if you have severe symptoms or you have a higher risk of flu complications. Symptoms to watch out for include:

  • Difficulty breathing or shortness of breath
  • Pain or pressure in the chest or abdomen
  • Sudden dizziness
  • Confusion
  • Severe or persistent vomiting
  • Flu-like symptoms that improve but then return with fever and worse cough

If you have any of these symptoms, it’s important that you seek medical care right away.

Early treatment with antiviral drugs can help prevent serious flu complications.


The flu is a very contagious disease that has a flu season during the colder months in the United States.

Flu season typically runs from October until May, with it usually peaking anywhere from December through February.

The data for the annual flu season is collected and analyzed by the CDC and released to the public weekly.

If you are a healthy adult, you will most likely not need to seek medical attention for the flu unless you have severe symptoms or are at a higher risk of developing complications.

The best way to prevent the flu is by getting a flu vaccine each year as they are safe, effective, and available for most people over six months of age or older.

Other preventive measures are also listed above. If you have any more questions about the flu or flu season, please consult your doctor or health care provider.

References, Studies and Sources:


GoodRx Health

Vaccinate Your Family

MN Department of Health

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