The flu is a respiratory infection caused by a virus (germ). Influenza occurs most often during the winter and easily spreads from person to person. The "flu season" in the Northern hemisphere runs from October to May and usually peaks between December and February.
Most people who get influenza feel sick for a week or two and recover. In some people, the flu leads to more serious lung infections or to worsening of underlying conditions, such as heart failure or emphysema.
Many cold and flu symptoms are similar. Both the common cold and the flu are caused by viruses.
There are some differences with influenza. Symptoms of influenza often hit suddenly and cause you to become weaker and weaker. While the more uncomfortable symptoms of flu generally last from three to seven days, the dry cough and fatigue of influenza can last two to three weeks. Signs that influenza is getting worse include increasing degree of fever, and shortness of breath. If you think that your illness is getting worse, contact your doctor right away.
Symptoms of colds and flu
|Fever||Adults-rare; children-sometimes||High fever (100°F up to 104°F in adults and 106°F in children); can last 3 to 4 days)|
|Runny nose||Common (Nasal discharge may have a yellow- or green-colored tint. This does not mean you have a bacterial infection.)||Sometimes|
|Headache||Sometimes (usually mild)||Common (usually severe)|
|Body aches and pains||Sometimes (usually mild)||Common (can be severe)|
|Fatigue (tiredness), weakness||Sometimes (usually mild)||Common (can last up to 2-3 weeks)|
|Chills, sweating||Not common||Common|
|Nausea||Uncommon||Common in children|
|Loss of appetite||Sometimes||Common|
|Cough||Common (mild to moderate)||Common (can be intense, severe)|
|Chest congestion, discomfort||Common (mild to moderate)||Common (can be severe)|
|Vomiting||Not common||Sometimes (more in children)|
|Diarrhea||Not common||Sometimes (more in children)|
|Complications||Sinus congestion, earache||Bronchitis, pneumonia (can be life-threatening)|
It’s important to take flu medicines very early (within 48 hours of coming down with symptoms), so you should contact your doctor as soon as you think you may have the flu.
Most people with influenza who are otherwise healthy do not need special drugs or treatments. If you have the flu, you should:
Note: Adults should not give aspirin to children or adolescents with fevers due to the association with Reye's syndrome, a rare disorder that causes brain and liver damage.
If you are seriously ill, your doctor might order an antiviral drug for you. Antiviral drugs for influenza include oseltamivir phosphate (Tamiflu®); zanamivir (Relenza®); peramivir (Rapivap®); and baloxavir (Xofluza®).
This drug is approved to treat influenza in patients who are two weeks of age and older, and it works best in people who have had the flu for fewer than two days. It is also approved to prevent flu in patients who are one year of age and older. There is a generic version of this product available, but it costs nearly as much as the brand name. Potential side effects include nausea, vomiting, nosebleeds, headaches and tiredness.
This drug is approved to treat flu in patients seven years old and older, and to prevent flu in patients who are five and older. This product is inhaled and not recommended for people who have respiratory illnesses like COPD or asthma. Common side effects include headaches, nausea, diarrhea, nose irritation and vomiting.
This drug is approved to treat flu in people 2 years old and older. This product is given into the vein (intravenously) by a healthcare provider. A common side effect from peramivir is diarrhea.
This drug, a pill, is approved to treat flu in people 12 years old and older who are otherwise healthy and in people who are at higher risk of developing influenza-related complications. Common side effects are diarrhea, bronchitis, nausea and headaches.
The side effects mentioned for the above drugs are only the most common. There are other possible side effects. As with any type of medication, you might be allergic. Please discuss side effects with your doctor or pharmacist.
Amantadine and rimantidine have also been approved to treat influenza, but flu viruses are widely resistant to them.
What complications are associated with influenza (flu)?
Infections from bacteria are more likely when you have influenza. Healthcare providers treat these bacterial infections with antibiotic drugs. Common secondary infections include:
Yes. If you get the flu vaccine, you are likely to be protected from the flu for the duration of the flu season. The vaccine is given as a shot or a nasal spray. You must get the vaccine every year in the fall to be protected. Sometimes the vaccine does not prevent you from getting the flu but makes the flu less severe if you do get it. The vaccine is safe, even for pregnant women. You can’t get the flu from the ‘flu shot.’
In addition, some of the antivirals (Relenza and Tamiflu) given to treat flu can be given to prevent flu in people who are in close contact with people who actually have the flu.
Because the flu is so contagious, you can do other things that may help you prevent getting or spreading the flu:
It’s recommended that everyone 6 months or older should get an influenza vaccine each year. You will protect yourself and other people around you. People who have any of the following conditions are at high risk of becoming seriously ill from influenza :
You also have a higher risk of becoming seriously ill from influenza if you:
If you work in a healthcare facility, you may transmit influenza to patients and other workers, but you are not at a higher risk of becoming seriously ill. The recommendation from the Centers for Disease Control and Prevention is that everyone over the age of 6 months gets a flu vaccine if there are no contraindications. This includes individuals who are not at high risk.
You shouldn’t get the influenza shot if you are
There is an option to get the nasal flu vaccine (administered through your nose). The following groups of people shouldn't get the nasal flu vaccine:
(Please remember that the above list is for people who should not receive the NASAL flu vaccine. It does not refer to the flu shot.)
The best time to get the flu vaccine is in the early fall. It takes about 3 weeks for the vaccine to exert its protective benefits, so don’t delay receiving it.
People over 65 and those with chronic(long-term) illnesses have a hard time fighting influenza because the body’s system for fighting infections is often weakened by age and illness. In older people, influenza is also more likely to lead to:
Because of the importance of taking flu medicines within 48 hours of coming down with symptoms, call immediately if you think you have the flu. If you continue to feel unwell after you have been treated for the flu, you should call your doctor’s office. If you find yourself feeling better, and then getting sick again, you should also contact your doctor. The flu might have left you with some kind of secondary illness, like a sinus infection.
You are contagious for one day before starting feeling ill, and for 5 to 7 days while you have the flu symptoms. At the very least, you should stay at home until you are able to go 24 hours without taking something for fever. If you have other severe symptoms, such as incessant (non-stop) cough or shortness of breath, you should stay at home.
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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or healthcare provider. Please consult your healthcare provider for advice about a specific medical condition. This document was last reviewed on: 11/25/2019