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
- Native Americans
- 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
Though the annual influenza vaccine isn’t 100% effective, it’s still your best defense against the flu.
Common signs and symptoms of the flu include:
- Aching muscles
- Chills and sweats
- 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
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
- Worsening of existing medical conditions
- Severe weakness or muscle pain
Emergency signs and symptoms in children can include:
- Difficulty breathing
- Blue lips
- Chest pain
- Severe muscle pain
- Worsening of existing medical conditions
Flu: When to see a doctor?
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.
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 are also 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 your immune system. This can make it easier for you to catch the flu and may also increase your risk of developing complications.
- 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 your risk of influenza complications.
- Race. Native American people may have an increased risk of influenza complications.
- Aspirin use under age 19. People who are younger than 19 years of age and receiving long-term aspirin therapy are at risk of developing Reye’s syndrome if infected with influenza.
- Pregnancy. Pregnant women are more likely to develop influenza complications, particularly in the second and third trimesters. Women are more likely to develop influenza-related complications up to two weeks after delivering their babies.
- Obesity. People with a body mass index (BMI) of 40 or more have an increased risk of flu 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:
- Asthma flare-ups
- Heart problems
- Ear infections
- Acute respiratory distress syndrome
Pneumonia is one of the most serious complications. For older adults and people with a chronic illness, pneumonia can be deadly.
Flu vaccination is especially important this season because the flu and coronavirus disease 2019 (COVID-19) cause similar symptoms. Flu vaccination could reduce symptoms that might be confused with those caused by COVID-19. Preventing the flu and reducing the severity of flu illness and hospitalizations could also lessen the number of people needing to stay in the hospital.
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 childcare 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.
- During the COVID-19 pandemic, 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. 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 facemask when around people outside your household.