Influenza is a viral infection that attacks your
respiratory system - your nose, throat and
lungs. Influenza is commonly called the flu, but
it's not the same as stomach "flu" viruses that
cause diarrhea and vomiting.
For most people, the flu resolves on its own. But
sometimes, influenza and its complications can
be deadly. People at higher risk of developing flu
complications include:
- Young children under age 5, and especially those under 6 months
- Adults older than age 65
- Residents of nursing homes and other long-term care facilities
- Pregnant women and women up to two weeks after giving birth
- People with weakened immune systems
- People who have chronic illnesses, such as asthma, heart disease, kidney disease, liver disease and diabetes
- People who are very obese, with a body mass index (BMI) of 40 or higher
Symptoms
At first, the flu may seem like a common cold with a runny nose, sneezing and sore throat. But colds usually develop slowly, whereas the flu tends to come on suddenly. And although a cold can be a bother, you usually feel much worse with the flu.
Common signs and symptoms of the flu include:
- Fever
- Aching muscles
- Chills and sweats
- Headache
- Dry, persistent cough
- Shortness of breath
- Tiredness and weakness
- Runny or stuffy nose
- Sore throat
- Eye pain
- Vomiting and diarrhea, but this is more common in children than adults
When to see a doctor
Most people who get the flu can treat themselves at home and often don't need to see a doctor.
If you have flu symptoms and are at risk of complications, see your doctor right away. Taking antiviral drugs may reduce the length of your illness and help prevent more-serious problems.
If you have emergency signs and symptoms of the flu, get medical care right away. For adults, emergency signs and symptoms can include:
- Difficulty breathing or shortness of breath
- Chest pain
- Ongoing dizziness
- Seizures
- Worsening of existing medical conditions
- Severe weakness or muscle pain
Emergency signs and symptoms in children can include:
- Difficulty breathing
- Blue lips
- Chest pain
- Dehydration
- Severe muscle pain
- Seizures
- Worsening of existing medical conditions
Causes
Influenza viruses travel through the air in droplets when someone with the infection coughs, sneezes or talks. You can inhale the droplets directly, or you can pick up the germs from an object - such as a telephone or computer keyboard - and then transfer them to your eyes, nose or mouth.
People with the virus are likely contagious from about a day before symptoms appear until about five days after they start. Children and people with weakened immune systems may be contagious for a slightly longer time.
Influenza viruses are constantly changing, with new strains appearing regularly. If you've had influenza in the past, your body has already made antibodies to fight that specific strain of the virus. If future influenza viruses are similar to those you've encountered before, either by having the disease or by getting vaccinated, those antibodies may prevent infection or lessen its severity. But antibody levels may decline over time.
Also, antibodies against influenza viruses you've encountered in the past may not protect you from new influenza strains that can be very different viruses from what you had before.
Risk factors
Factors that may increase your risk of developing the flu or its complications include:
- Age. Seasonal influenza tends to target children 6 months to 5 years old, and adults 65 years old or older.
- Living or working conditions. People who live or work in facilities with many other residents, such as nursing homes or military barracks, are more likely to develop the flu. People who are staying in the hospital also are at higher risk.
- Weakened immune system. Cancer treatments, anti-rejection drugs, long-term use of steroids, organ transplant, blood cancer or HIV/AIDS can weaken the immune system. This can make it easier to catch the flu and may also increase the risk
- Chronic illnesses. Chronic conditions, including lung diseases such as asthma, diabetes, heart disease, nervous system diseases, metabolic disorders, an airway abnormality, and kidney, liver or blood disease, may increase the risk of influenza complications.
Complications
If you're young and healthy, the flu usually isn't serious. Although you may feel miserable while you have it, the flu usually goes away in a week or two with no lasting effects. But children and adults at high risk may develop complications that may include:
- Pneumonia
- Bronchitis
- Asthma flare-ups
- Heart problems
- Ear infections
- Acute respiratory distress syndrome
It may be possible to get a COVID-19 vaccine at the same time as your flu vaccine.
This year's seasonal flu vaccine provides protection from the four influenza viruses that are expected to be the most common during the year's flu season. This year, the vaccine will be available as an injection and as a nasal spray.
The nasal spray isn't recommended for some groups, such as:
- Children under 2
- Adults 50 and older
- Pregnant women
- Children between 2 and 17 years old who are taking aspirin or a salicylate-containing medication
- People with weakened immune systems
Controlling the spread of infection
The influenza vaccine isn't 100% effective, so it's also important to take several measures to reduce the spread of infection, including:
- Wash your hands. Washing your hands often with soap and water for at least 20 seconds is an effective way to prevent many common infections. Or use alcohol-based hand sanitizers if soap and water aren't available.
- Avoid touching your face. Avoid touching your eyes, nose and mouth.
- Cover your coughs and sneezes. Cough or sneeze into a tissue or your elbow. Then wash your hands.
- Clean surfaces. Regularly clean often touched surfaces to prevent spread of infection from touching a surface with the virus on it and then your face.
- Avoid crowds. The flu spreads easily wherever people gather - in child care centers, schools, office buildings, auditoriums and public transportation. By avoiding crowds during peak flu season, you reduce your chances of infection.
Also avoid anyone who is sick. And if you're sick, stay home for at least 24 hours after your fever is gone so that you lessen your chance of infecting others.
Both COVID-19 and the flu may be spreading at the same time. Your local health department and the CDC may suggest other precautions to reduce your risk of COVID-19 or the flu if you haven't been fully vaccinated. For example, you may need to practice social distancing (physical distancing) and stay at least 6 feet (2 meters) from others outside your household. You may also need to wear a cloth face mask when indoors with people outside your household and when outdoors in crowded areas. If you're fully vaccinated and are in an area with a high number of new COVID-19 cases in the last week, the CDC also recommends wearing a mask indoors in public and outdoors in crowded areas or when you're in close contact with unvaccinated people.