Influenza (flu) - Symptoms and causes

The flu, commonly known as influenza, is a respiratory infection that affects the nose, throat, and lungs. The flu is caused by a virus. Influenza viruses differ from the "stomach flu" viruses, which cause diarrhea and vomiting. Most persons with the flu recover on their own. However, influenza and its consequences can be fatal.

Seasonal flu shots can help avoid the flu. Although the vaccine is not completely effective, it reduces the risk of serious flu complications. This is especially true for persons who are highly susceptible to flu complications.

Aside from getting vaccinated, there are other precautions you may do to help avoid respiratory infections like the flu. You can clean and sanitize surfaces, wash your hands, and circulate the air around you.

Flu viruses spread rapidly during particular times of the year in both the Northern and Southern hemispheres. These are the flu seasons. The flu season in the North lasts from October to March, with rare cases extending into May. The flu season in the South normally lasts from April until September.

Flu symptoms appear roughly 1 to 4 days after being exposed to the virus. Symptoms usually appear soon.

Fever occurs, although not always.

Chills.

Headache.

Muscle ache.

There's no appetite.

Painful or wet eyes.

Other influenza symptoms include:

Cough.

Sore throat.

A runny or congested nose.

Fatigue and weakness.

Wheezing and lack of breath.

These symptoms are common, but not everyone experiences them. In youngsters, symptoms may manifest more broadly as being fussy or irritable. Children are also more likely than adults to experience diarrhea, vomiting, and stomach distress.

Most people who catch the flu may treat it at home and do not need to see a doctor.

However, if you have flu symptoms and are at risk of complications, contact your healthcare provider right soon. Antiviral treatment works best when used as soon as feasible. That usually implies within two days of your symptoms appearing. Taking medication within that time limit may minimize the duration of your condition.

If you have flu-related emergency symptoms, seek medical attention straight soon. For adults, emergency symptoms may include:

Problems breathing or shortness of breath.

Chest discomfort or pressure.

Ongoing dizziness.

Trouble waking up or disorientation.

Dehydration.

Seizures.

Existing medical issues become worse.

Extreme weakness or muscle discomfort.

Rapid breathing or ribs that draw in with each inhale.

Lips and nail beds can be gray or blue.

No tears when crying, dry mouth, and no urge to urinate.

Symptoms such as fever or cough that improve briefly before returning or worsening.

Influenza is caused by viruses. When an infected person coughs, sneezes, or speaks, the viruses spread through the air in droplets. You can inhale the droplets immediately. Alternatively, you can contract the virus by contacting an object, such as a computer keyboard, then touching your eyes, nose, or mouth.

It is possible to spread the virus to people from about a day before symptoms develop to 5 to 7 days after they begin. This is known as being contagious. Children and persons with lower immune systems may be contagious for a somewhat longer period.

Influenza viruses are continually evolving, with new strains developing frequently. However, the vaccines available each year are designed to match the flu virus strains that are most likely to circulate that season. The protection provided by these immunizations lasts for months in most people.

There are several variables that can increase your chance of contracting the flu virus or developing complications from a flu infection.

Treatments or medical conditions can increase the chance of developing flu or flu complications, including:

The immune system is weakened. An immune system that does not promptly remove the flu virus increases the risk of contracting the flu or developing flu complications. A reduced immune system might be present at birth or be caused by an illness, therapy, or medication.

Chronic sickness. Chronic illnesses can raise the risk of influenza complications. Examples include asthma and other lung ailments, diabetes, heart disease, nervous system diseases, a history of stroke, metabolic abnormalities, airway issues, and kidney, liver, or blood disease.

Aspirin treatment. Young people on long-term aspirin are at risk of getting Reye's syndrome if infected with the flu virus.

Other factors that can influence the likelihood of acquiring flu or being critically unwell with flu include:

Age. Seasonal influenza has a worse prognosis in young children, particularly those aged 2 and less. Adults above the age of 65 also have lower outcomes.

A population group. People in the United States who are Native American or Alaska Native, Black, or Latino may be more likely to require hospitalization for influenza.

Living circumstances. People who live in facilities with a large number of people, such as nursing homes, are more prone to contract the flu.

Pregnancy. People who are pregnant are more susceptible to have influenza complications, especially in the second and third trimesters.

Obesity. People with a BMI of 40 or higher are more likely to develop flu complications.

If you are young and healthy, the flu is usually not a big deal. Although you may feel terrible while you have it, the flu normally passes in a week or two with no lingering symptoms. People who are at high risk, however, may develop additional health problems as a result of the flu, known as complications.

Another infection may arise as a result of the flu. This includes diseases like croup and sinus or ear infections. Lung infections are another consequence. After catching the flu, you may develop an infection of your heart muscle or lining. In some situations, patients may develop central nervous system infections.

Acute respiratory distress syndrome.

Rhabdomyolysis refers to muscular injury, whereas myositis refers to muscle swelling.

Toxic shock syndrome.

Chronic illnesses, such as asthma or kidney disease, worsen.

The risk of contracting the flu. If the flu vaccine is administered later in pregnancy, it also protects the newborn from the virus.

The danger of being really ill from the flu and being admitted to the hospital.

The danger of dying from the flu.

The 2026-2027 seasonal flu vaccines in the United States protect against three influenza viruses that researchers predict would be the most common this flu season.

The vaccination is offered in three forms: injection, jet injector, and nasal spray.

If you are allergic to eggs, you can still obtain the flu vaccine.

If a kid aged 6 months to 8 years has never received a flu vaccine or has received only one dose, he or she may require two doses administered at least four weeks apart. Following that, the youngster will receive a single annual dosage of the flu vaccine. Consult with your child's healthcare provider.

If you have had a serious reaction to a previous flu vaccine, see your healthcare provider before receiving another. People who have had Guillain-Barre syndrome should also consult with a doctor before obtaining the flu vaccine. If you have a cold or are not feeling well, you may still be able to obtain a flu shot. However, if you are extremely ill, see your healthcare provider to see if you should postpone having the vaccine.

Flu vaccines are typically administered based on age. The flu vaccination is often administered to older children and adults via a muscle in the arm. Younger youngsters may receive the flu shot in their thigh muscle.

High-dose, recombinant, or adjuvanted flu vaccinations may be a possibility. People above the age of 65 can receive these immunizations. These vaccines may also be accessible to patients aged 18 and above who have had a solid organ transplant and are taking medication to suppress their immune response. These immunizations may allow persons in these groups to avoid hospitalization due to influenza.

People aged 50 and up may be able to get a flu vaccination that employs messenger RNA (mRNA) to protect against the flu. This form of vaccine instructs the body how to produce proteins from the surface of flu viruses but not the rest of the virus. As a result, it cannot cause you to contract the flu. The mRNA instructions only apply to the flu virus's surface proteins. When you develop an infection, your body sees this first. Following immunization, your immune cells begin producing and expressing the proteins on their surfaces. This causes your body to produce antibodies that are prepared to respond to an actual infection.

In the United States, if you are an adult under the age of 65, you can receive your immunization via a device known as a jet injection. Instead of a needle, this device administers the vaccination via a high-pressure, narrow stream of fluid via the skin.

In the United States, a seasonal flu nasal spray is approved for people aged 2 to 49. If the nasal spray is an option for you or someone you care about, you may be able to get it without having to see a doctor in person.

The nasal spray flu vaccine is not recommended for specific individuals, including:

Individuals who have severe asthma or are already wheezing.

Individuals who previously experienced a severe adverse reaction to a flu shot.

Individuals who are pregnant.

Young people who take salicylate-containing medications, such as aspirin.

People with extremely compromised immune systems, as well as their caregivers or intimate contacts.

Children aged 2 to 4 years who have been diagnosed with asthma or wheezing during the last 12 months.

People who recently used antiviral medication for the flu.

People who have a cochlear implant or are at risk of having a cerebrospinal fluid leak.

Check with your doctor to determine if you need be concerned about having a nasal spray flu vaccine.

Controlling the spread of infections

You can take the following precautions to reduce the spread of infection:

Wash your hands. If possible, use soap and water to wash for at least 20 seconds. Alternatively, use a hand sanitizer containing at least 60% alcohol.

Do not touch your face. Avoid touching your eyes, nose, or mouth. These are sites where germs can enter the body.

Cover your coughs and sneezes. Cough or sneeze into a tissue or elbow. Then, wash your hands.

Clean the surfaces. Clean frequently touched surfaces on a regular basis to avoid infection from spreading from a surface with the virus on it to your face.

Also, strive to reduce your chances of coming into contact with the influenza virus. The flu spreads easily anywhere people congregate. When the flu is spreading, try to keep some distance between yourself and others when indoors, especially in locations with poor air movement. Try to avoid those who are ill or showing flu symptoms. If you have symptoms, try to stay at home as much as possible.

Learn about the history of major disease outbreaks, epidemics, and pandemics, as well as how vaccines and research affected numerous infectious diseases.