Also known as the flu, influenza is a highly contagious respiratory infection that spreads easily from person to person, mainly when an infected person coughs or sneezes. Influenza attacks the respiratory system — your nose, throat and lungs. Influenza, commonly called the flu, is not the same as the stomach "flu" viruses that cause diarrhea and vomiting.
Approximately 10 percent to 20 percent of Americans come down with the disease during each flu season, which typically lasts from November to March. Common symptoms include fever, cough, headaches, and extreme fatigue.
Each winter, millions of people suffer from influenza, which is a highly contagious infection. Influenza spreads easily from person to person, mainly when an infected person coughs or sneezes. Viruses that infect the nose, throat, and lungs cause influenza, which is also known as the flu. It is usually a mild disease in healthy children, young adults, and middle-aged people. However, influenza can be life threatening in older adults and in people of any age who have chronic illnesses, such as diabetes or heart, lung, or kidney diseases.
Influenza is a respiratory infection that can be caused by a variety of viruses. It differs in several ways from the common cold, which is a respiratory infection that is also caused by viruses. For example, people with colds rarely get fevers, headaches, or suffer from the extreme exhaustion that influenza viruses can cause.
Influenza outbreaks usually begin suddenly and occur mainly in the late fall and winter. Influenza then spreads through communities, creating an epidemic. During the epidemic, the number of cases peaks in about 3 weeks and subsides after another 3 or 4 weeks. Half the population of a community may be affected. Schools are an excellent place for influenza viruses to attack and spread. Therefore, families with school-age children have more infections than other families, with an average of one-third of the family members becoming infected each year.
You can get the flu if someone around you who has the disease coughs or sneezes. You can also get influenza simply by touching a surface, like a telephone or doorknob, that has been contaminated by someone who has influenza. The viruses can pass through the air and enter your body through your nose or mouth, or if you've touched a contaminated surface, they can pass from your hand to your nose or mouth. You are at greatest risk of getting infected in highly populated areas, such as in crowded living conditions and in schools.
The flu virus is contained in the millions of tiny droplets that come out of the nose and mouth when someone coughs or sneezes.
These droplets typically spread about one meter. They hang suspended in the air for a while before landing on surfaces, where the virus can survive for up to 24 hours.
Anyone who breathes in the droplets can catch flu. And anyone who touches the surfaces the droplets have landed on can also catch flu if they pick up the virus on their hands and then touch their nose or mouth.
Everyday items at home and in public places can easily become contaminated with traces of flu virus including food, door handles, the remote control, handrails, telephone handsets and computer keyboards.
So, it's very important to wash your hands frequently to prevent catching and spreading flu.
If you become infected with a flu virus your body will produce antibodies against it. Antibodies are proteins that recognition and fight off germs that have invaded your body.
Your antibodies will remember this flu virus and fight it if it invades your body again.
But, over time the flu virus can change into a different version or strain, which means your body may not recognize it and you can catch flu again.
When the virus changes to a new strain that people have little or no resistance to, it can cause a flu pandemic, which means it can spread globally. This is what happened in the swine flu pandemic of 2009.
The global flu epidemic (pandemic) of 1918, killed tens of millions of people.
Factors that may increase your risk of developing influenza or its complications include:
Age. Seasonal influenza tends to target young children and people over 65. The pandemic H1N1 virus that surfaced in 2009, however, appeared to be most common in teenagers and young adults.
Occupation. Health care workers and child care personnel are more likely to have close contact with people infected with influenza.
Living conditions. People who live in facilities along with many other residents, such as nursing homes or military barracks, are more likely to develop influenza.
Weakened immune system. Cancer treatments, anti-rejection drugs, corticosteroids and HIV/AIDS can weaken your immune system. This can make it easier for you to catch influenza and may also increase your risk of developing complications.
Chronic illnesses. Chronic conditions, such as asthma, diabetes or heart problems, may increase your risk of influenza complications.
Pregnancy. Pregnant women are more likely to develop influenza complications, particularly in the second and third trimesters.
Main article: Flu Symptoms
It's easy to confuse a common cold with the symptoms of influenza (also known as the flu). Cold symptoms are usually milder and don't last as long as influenza symptoms. Fever, chills, dry cough, and sore throat are the most common signs and symptoms of influenza. If you become infected with the influenza virus, you will usually feel symptoms 1 to 4 days later. It is important to note that you can spread the disease to others before your influenza symptoms appear and for another 3 to 4 days after they appear.
These common influenza symptoms start quickly and can include:
Fever
Chills
Dry cough
Sore throat
Runny or stuffy nose
Headache
Muscle aches
Extreme fatigue.
Typically, the fever will begin to decline on the second or third day of the illness.
Although nausea, vomiting, and diarrhea can accompany influenza symptoms, especially in children, gastrointestinal symptoms rarely occur. The illness that people call "stomach flu" is not influenza.
Complications related to symptoms of influenza in adults can occur if they develop a bacterial infection, which can cause pneumonia in already weakened lungs. However, the flu virus alone can also cause pneumonia. Complications due to influenza usually appear after you start to feel better. After a brief period of improvement, you may suddenly get symptoms, such as:
High fever
Shaking chills
Chest pain with each breath
Coughing that produces thick, yellow-green mucus.
Pneumonia can be a serious and sometimes life-threatening condition. If you have any of these symptoms, you should contact your healthcare provider immediately to get the appropriate treatment.
Children and teenagers can develop the same flu complications as adults, and children are also at risk for developing Reye's syndrome.
Reye's syndrome is a condition that affects the nerves. It can develop in children and teenagers who are recovering from the flu. Although Reye's syndrome begins with nausea and vomiting, the progressive mental changes (such as confusion or delirium) cause the greatest concern. Reye's syndrome often begins in young people after they take aspirin to get rid of fever or pain. Although very few children develop Reye's syndrome, parents should consult a healthcare provider before giving aspirin or products that contain aspirin to children. Acetaminophen does not seem to be connected with Reye's syndrome.
Other complications of the flu that can affect children are:
Convulsions caused by fever
Croup
Ear infections, such as otitis media.
Newborn babies recently out of intensive care units are particularly vulnerable to suffering from flu complications.
First, individuals should be sure they are not members of a high-risk group that is more susceptible to getting severe flu symptoms. Check with your physician if you are unsure if you are a higher-risk person. Home care is recommended by the CDC if a person is normally healthy with no underlying diseases or conditions (for example, asthma, lung disease, pregnant, or immunosuppressed).
Usually, you'll need nothing more than bed rest and plenty of fluids to treat the flu. Increasing liquid intake, warm showers, and warm compresses, especially in the nasal area, can reduce the body aches and reduce nasal congestion. Nasal strips and humidifiers may help reduce congestion, especially while trying to sleep. But in some cases, your doctor may prescribe an antiviral medication, such as oseltamivir (Tamiflu) or zanamivir (Relenza). If taken soon after you notice symptoms, these drugs may shorten your illness by a day or so and help prevent serious complications.
Oseltamivir is an oral medication. Zanamivir is inhaled through a device similar to an asthma inhaler and shouldn't be used by anyone with respiratory problems, such as asthma and lung disease. Antiviral side effects may include nausea and vomiting. Oseltamivir has also been associated with delirium and self-harm behaviors in teenagers.
Some strains of influenza have become resistant to oseltamivir and to amantadine, which is an older antiviral drug.
Some physicians recommend nasal irrigation with saline to further reduces congestion; some recommend nonprescription decongestants. Fever can be treated with over-the counter acetaminophen (Tylenol) or ibuprofen (Motrin and others) (read labels for safe dosage). Cough can be suppressed by cough drops and over-the-counter cough syrup. If an individual's symptoms at home get worse, their doctor should be notified.
Before flu season begins, scientists prepare a new influenza vaccine made from inactivated (killed) flu viruses, which cannot cause infection. The preparation is based on the flu viruses that are currently in circulation and on viruses that are expected to circulate the following winter. The influenza vaccine is a yearly vaccination because the viruses that cause the disease change every year.
You can get the vaccine at:
Your doctor's office
A local clinic
Work (in many communities)
Supermarkets
Drugstores.
It is important to note that you must get the influenza vaccine every year because the viruses on which it is based change every year.
Scientists make a different influenza vaccine every year because the strains of flu viruses change from year to year. Nine to ten months before the flu season begins, scientists prepare a new influenza vaccine made from inactivated (killed) flu viruses. Because the viruses are killed, they cannot cause infection. The influenza vaccine preparation is based on the flu viruses that are in circulation at the time and on the viruses that are expected to circulate the following winter.
It is important to note that an unpredicted new strain of the flu virus may appear after the influenza vaccine has been made and distributed to doctors' offices and clinics. This means that even if you do get the influenza vaccine, you still may get infected. However, if this happens, the disease is usually milder because the influenza vaccine will still give you some protection.
Until recently, you could get the influenza vaccine only as an injection (flu shot). However, in 2003, the U.S. Food and Drug Administration (FDA) approved a nasal spray form of the influenza vaccine called FluMist, which you can get from your healthcare provider. The FDA approved it for use in healthy people who are 5 to 49 years of age.
You should not use FluMist if:
You have certain lung conditions, including asthma, or heart conditions
You have metabolic disorders, such as diabetes or kidney dysfunction
You have an immunodeficiency disease or you are on immunosuppressive treatment
You have had Guillain-Barré syndrome
You are pregnant
You have a history of allergy or hypersensitivity to any of the parts of FluMist or to eggs
You are a child or teenager who regularly takes aspirin or products containing aspirin.
Your immune system takes time to respond to the influenza vaccine. Therefore, you should get vaccinated 6 to 8 weeks before flu season begins in November to prevent getting infected or to reduce the severity of flu if you do get it. However, flu season usually lasts until March, so it is not too late to get the influenza vaccine after the season has begun. The influenza vaccine itself cannot cause the flu, but you could become exposed to the virus by someone else and get infected soon after you are vaccinated.
Approximately 5 percent to 10 percent of people who get the influenza vaccine will have mild side effects for about a day after vaccination. The most common side effect in children and adults is soreness at the site of the vaccination. Other side effects, especially in children who previously have not been exposed to the flu virus, include:
Fever
Tiredness
Aches
Headache
Sore muscles
Soreness, redness, or swelling where the shot was given
These side effects of the influenza vaccine may begin 6 to 12 hours after vaccination and may last for up to 2 days. Almost all people who receive influenza vaccine have no serious problems from it. However, on rare occasions, flu vaccination can cause serious problems, such as severe allergic reactions. As of July 1, 2005, people who think that they have been injured by the flu shot can file a claim for compensation from the National Vaccine Injury Compensation Program (VICP).
Viruses used for producing the influenza vaccine are grown in chicken eggs and then killed with a chemical so that they can no longer cause an infection. As a result, the influenza vaccine may contain some egg protein, which can cause an allergic reaction. If you are allergic to eggs or have ever had a serious allergic reaction to the influenza vaccine, the Centers for Disease Control and Prevention (CDC) recommends that you consult with your healthcare provider before getting vaccinated.
Although influenza vaccines don't cause influenza, some people have complained that they got the the flu after the vaccination.
After getting a flu vaccine, many people experience symptoms such as a runny nose or achiness for a day or so. That means the immune system is responding, and it's a good sign. It means your body is processing this material (in the vaccine), but it's not flu.
Flu vaccine prevents influenza, not illnesses caused by other germs. There are multiple respiratory viruses out there, so it's not impossible to get the vaccine and still get flu. The vaccine is generelly 70% to 80% effective in healthy adults, less in older people.
The viruses in the nasal-spray vaccine are weakened and do not cause severe symptoms often associated with influenza illness. (In clinical studies, transmission of vaccine viruses to close contacts has occurred only rarely.)
In children, side
effects from LAIV (FluMist) can include:
runny nose
wheezing
headache
vomiting
muscle aches
fever
In adults, side effects from LAIV (FluMist) can include:
runny nose
headache
sore throat
cough
People who are in any of the following groups, or live in a household with someone who is, should get the influenza vaccine:
You are 50 years of age or older
You have chronic diseases of your heart, lungs, or kidneys
You have diabetes
Your immune system does not function properly
You have a severe form of anemia
You will be more than 3 months pregnant during the flu season
You live in a nursing home or other chronic-care housing facility
You are in close contact with children 23 months of age or younger.
The CDC recommends that children 6 months to 23 months of age get the influenza vaccine. Children and teenagers (2 to 18 years of age) should get the influenza vaccine if they are taking long-term aspirin treatment, as they may be at risk of developing Reye's syndrome following a flu infection. Children should also get the influenza vaccine if they live in a household with someone in the above-mentioned groups. Healthcare providers and volunteers should get the influenza vaccine if they work with people in any of these groups.
There are some people who should not get a flu vaccine without first consulting a physician. These include:
People who have a severe allergy to chicken eggs.
People who have had a severe reaction to an influenza vaccination.
Children younger than 6 months of age (influenza vaccine is not approved for this age group), and
People who have a moderate-to-severe illness with a fever (they should wait until they recover to get vaccinated.)
People with a history of Guillain–Barré Syndrome (a severe paralytic illness, also called GBS) that occurred after receiving influenza vaccine and who are not at risk for severe illness from influenza should generally not receive vaccine. Tell your doctor if you ever had Guillain-Barré Syndrome. Your doctor will help you decide whether the vaccine is recommended for you.