Symptoms of Swine Flu (H1N1 Flu)

Symptoms of swine flu, which is caused by the H1N1 virus, are like those of any seasonal flu and include fever, cough, runny nose, sore throat, body aches, chills, and fatigue. Although some people still talk about swine flu, it's important to keep in mind that now swine flu is considered another regular type of human flu virus, similar to other seasonal flu viruses.

In 2009, the big difference was that when the swine influenza A virus known as H1N1 first appeared, it was new and most people didn't have any immunity to it. That's why it so easily became a pandemic virus and spread all over the world. Now this strain is included in the annual flu vaccine.

h1n1 swine flu symptoms
Illustration by Verywell

Frequent Symptoms

Like other seasonal flu viruses, common symptoms of swine flu (H1N1) develop between one and three days after you've been infected and can include:

  • Fever, which is usually high, but is sometimes absent
  • Cough
  • Runny or stuffy nose
  • Sore throat
  • Body aches
  • Headache
  • Chills
  • Fatigue or tiredness, which can be extreme
  • Diarrhea and vomiting occasionally, but more commonly seen than with other strains of flu

The H1N1 strain is now included in seasonal influenza vaccines.

Serious Symptoms

Serious symptoms are rarer. In children, they can include:

  • Fast breathing or difficulty breathing
  • Bluish or gray skin color
  • Not drinking enough fluids
  • Severe or persistent vomiting
  • Not waking up or not interacting
  • Irritability so great that your child does not want to be held
  • Flu-like symptoms get better but then come back with fever and worse cough
  • Rash with a fever

In adults, serious symptoms include:

  • Difficulty breathing
  • Chest pain or pressure
  • Abdominal pain or pressure
  • Dizziness
  • Confusion
  • Vomiting that's severe or won't stop
  • Flu-like symptoms get better but then come back with fever and worse cough

If you notice these, don't panic right away. It's important to coordinate with a healthcare provider or your medical team for prompt attention, and they can help you resolve the issue and its underlying cause.


Most people who get swine flu recover within a few days to two weeks after first having symptoms, but some people may develop complications.

H1N1 complications are most likely to occur if you:

  • are pregnant
  • are younger than 5 or older than 65 years old
  • have a chronic illness such as asthma, emphysema, diabetes, or heart disease

Potential complications include:

  • Worsening of a chronic condition
  • Pneumonia
  • Bronchitis
  • Ear infection
  • Confusion
  • Seizures
  • Respiratory failure

When to See a Healthcare Provider

Most normally healthy people can recover from the flu at home and prevent spreading it by avoiding other people. However, if you have a chronic illness like asthma, diabetes, or heart disease or have a suppressed immune system and you think you have the flu, you should see your healthcare provider so he or she can properly diagnose you and treat your symptoms accordingly.

You may get a course of antiviral medications that are used for high-risk people to help lessen the length and severity of your illness.

H1N1 Swine Flu Healthcare Provider Discussion Guide

Get our printable guide for your next healthcare provider's appointment to help you ask the right questions.

Doctor Discussion Guide Man

You should seek emergency care if you or your child has any of the serious symptoms listed above and/or you're getting worse. This is especially true if you or your child has a chronic illness as well.

When to Seek Emergency Care for Infants

If your baby has the flu and the following symptoms occur, seek emergency care immediately.

  • Unable to eat
  • No tears when crying
  • Having difficulty breathing
  • Fewer wet diapers than normal

The flu can be a life-threatening disease for children, especially those 5 years of age and younger, people over 65, and those with chronic conditions, so getting medical care as soon as possible for these populations is important.

Frequently Asked Questions

  • What are the signs and symptoms of swine flu?

    The symptoms of swine flu (a.k.a. H1N1 virus) are similar to those of other types of influenza and may include:

    • Fever
    • Chills
    • Cough
    • Sore throat
    • Fatigue
    • Body aches
    • Headache
    • Stuffy or runny nose
    • Red, watery eyes
    • Diarrhea
    • Nausea or vomiting
  • How do swine flu symptoms differ from other types of flu?

    The one big difference between swine flu and other types of flu is that swine flu not only causes respiratory symptoms but can also sometimes affect the gastrointestinal tract, causing nausea, diarrhea, or vomiting.

  • How long after exposure do swine flu symptoms appear?

    The incubation period for swine flu is between one and four days.

  • How long do swine flu symptoms last?

    Symptoms of swine flu generally last for four to six days, but malaise and cough may persist for up to two weeks.

  • What are the possible complications of swine flu?

    Possible complications of swine flu include:

  • Who is at risk of severe illness from swine flu?

    Groups at high risk for severe H1N1 infection are more or less the same as any other type of flu and include people over 65 years of age, pregnant persons, infants and young children, and people with chronic medical conditions. During the swine flu pandemic of 2009, people with obesity and children under the age of five were disproportionately affected.

  • Is swine flu worse than seasonal flu?

    The general consensus is that it is not, neither in terms of infection rates, hospitalizations, nor flu-related deaths. Today, swine flu is largely considered a "normal" seasonal flu strain.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Dandagi GL, Byahatti SM. An insight into the swine-influenza A (H1N1) virus infection in humans. Lung India. 2011;28(1):34-8. doi:10.4103/0970-2113.76299

  2. Al hajjar S, Mcintosh K. The first influenza pandemic of the 21st century. Ann Saudi Med. 2010;30(1):1-10. doi:10.4103/0256-4947.59365

  3. Sullivan SG, Price OH, Regan AK. Burden, effectiveness and safety of influenza vaccines in elderly, paediatric and pregnant populations. Ther Adv Vaccines Immunother. 2019;7:2515135519826481. doi:10.1177/2515135519826481

  4. Jilani TN, Jamil RT, Siddiqui AH. H1N1 influenza. In: StatPearls [Internet}.

  5. Altayep KM, Ahmed HG, Tallaa AT, Alzayed AS, Alshammari AJ, Talla ATA. Epidemiology and clinical complication patterns of influenza A (H1N1 virus) in northern Saudi Arabia. Infect Dis Rep. 2017;9(2). doi:10.4081/idr.2017.6930

  6. Van Kerkhove MD, Vandemaele KAH, Shinde V, et al. Risk factors for severe outcomes following 2009 influenza a (H1N1) infection: a global pooled analysis. PLoS Med. 2011;8(7):e1001053. doi:10.1371/journal.pmed.1001053

  7. Why "swine flu" is now considered a normal, seasonal flu strain.

By Vincent Iannelli, MD
 Vincent Iannelli, MD, is a board-certified pediatrician and fellow of the American Academy of Pediatrics. Dr. Iannelli has cared for children for more than 20 years.