Updated on April 17, 2024.
Influenza, or the flu, can cause fever, headaches, body aches, sore throat, coughing, congestion, and lack of energy. But for some, the virus can be more dangerous, or even life-threatening. The flu has resulted in 9.3 to 41 million illnesses, up to 710,000 hospitalizations, and between 4,900 and 51,000 deaths each year between 2010 and 2023, the Centers for Disease Control and Prevention (CDC) estimates.
“The flu is a respiratory illness caused by the influenza virus," says Matthew Tincher, MD, an emergency medicine specialist with TriStar Horizon Medical Center in Dickson, Tennessee.
Symptoms can vary from mild to severe, but the sickness is different than the common cold, he adds. Cold and flu are caused by different viruses and accompanied by varying symptoms. Fever, body aches and weakness are common with the flu, but not as much with a cold. Usual cold symptoms include sneezing, stuffy nose and sore throat, all which come on gradually.
Anyone can catch the flu, but some populations are more likely to have serious reactions. Find out who is at the highest risk and which symptoms may need emergency care.
Who is most at risk for flu complications?
Children: Because their immune systems are weaker, children younger than 5—and especially those younger than 2—are vulnerable to dangerous influenza complications. Since 2010, between 7,000 and 26,000 children younger than 5 were hospitalized for issues related to the flu each year, according to the CDC.
Pregnant people: Pregnancy alters the immune system, heart and lungs, which can mean getting the flu during pregnancy puts people at a higher risk for severe symptoms and flu complications like pneumonia.
“Your physiology, blood pressure, blood flow and heart rate are all different during pregnancy," Tincher says.
This sensitivity lasts up to two weeks after giving birth. The flu can also cause problems for a developing fetus including premature delivery and fetal brain, spine and spinal cord defects. Getting a flu shot during pregnancy can provide some protection to newborns until they are old enough to be immunized at 6-months of age.
Adults 65 and older: As people age, their immune systems weaken. The CDC estimates between 70 percent and 85 percent of flu-related deaths occur in people older than 65. Older people make up 54 percent to 70 percent of seasonal flu hospitalizations.
“Their immune systems are not fully active, so it’s easier for them to pick up the virus,” Tincher says.
People with medical conditions: The flu weakens the body and can make existing health problems worse. For this reason, people with conditions like asthma and diabetes may have a harder time managing symptoms while they're under the weather. One example: Infections like the flu make it harder for people with diabetes to control blood sugar levels.
Influenza can also increase your heart attack risk, according to a January 2018 New England Journal of Medicine study. Results suggest adults were six times more likely to have a heart attack within a week of a flu diagnosis than one year before or after the sickness. About half of adults hospitalized during the 2017-2018 flu season had heart disease.
People with these conditions are also at greater risk for flu-related complications:
- Chronic lung diseases, like chronic obstructive pulmonary disease and cystic fibrosis
- Liver and kidney disorders
- Neurological (brain) conditions, like epilepsy and cerebral palsy
- Blood disorders, like sickle cell disease
- Diseases or medications that weaken your immune system, like cancer, HIV or steroids
- Severe obesity—body mass index of 40 or greater
If you experience flu-like symptoms and have any of these medical conditions, talk to your healthcare provider (HCP) about getting the proper treatment.
When is emergency care necessary?
Flu symptoms typically come on suddenly within one to four days of exposure to the virus. The illness can last anywhere from a few days to two weeks. Common symptoms include a cough, chills, headaches, fatigue, muscle aches and sore throat. Not everyone with the flu will have a fever, but most do.
Some people will develop flu complications, however, like pneumonia, sepsis (a life-threatening reaction to an infection), sinus or ear infections and bronchitis. Both pneumonia and sepsis can be fatal, and need prompt medical treatment.
However most cases of influenza are mild and can be managed at home, without the help of a health professional, although some symptoms could signal the need for treatment. Adults should contact a HCP immediately for symptoms like:
- Difficulty breathing or shortness of breath
- Severe or persistent vomiting
- Chest or belly pain or pressure
- Sudden dizziness
- Confusion
- Dehydration
- Symptoms that get better, then return with fever and a worsened cough
"Not everybody with the flu needs to come to the emergency department," Tincher says. "The vast majority of healthy adults and children can get treatment for the flu in their doctor’s office." Can't get an appointment? Visit your local urgent care facility.
In infants and children, watch for trouble breathing, a fever accompanied by a rash, lack of tears when crying or skin that is bluish in color. “Children with the flu may show a decreased level of activity, a fever, rapid breathing or coughing,” says Tincher. If your young one has any of these symptoms, it could be a sign of a flu complication or severe illness, he adds.
“A healthy child should be active, smiling and playful,” Tincher says. If your child isn't interactive or is acting fussy and you think it could be due to the flu, he recommends heading to the emergency room.
What's the best way to prevent the flu?
The CDC recommends the flu vaccine, either the injectable vaccine or nasal spray depending on your age and health profile, for anyone 6 months and older. Children younger than 8 who have not been vaccinated before should receive two doses of the vaccine at least 28 days apart. If you're feeling under the weather or have an allergy to the vaccine or any of its ingredients, speak with your HCP before getting immunized. If necessary, your HCP can reschedule your vaccination appointment once your cold is gone and provide you with other tips for staying virus-free.
Research suggests vaccination typically reduces your flu risk by 40 percent to 60 percent, though its effectiveness varies year-to-year. Even if the flu shot doesn't prevent the flu, it can reduce severity of symptoms and protect against dangerous flu complications.
Flu outbreaks typically peak between December and February, but cases can occur as early as October and as late as May. The CDC recommends getting the flu vaccine before the end of October, but even vaccinations given in January or later can help safeguard against sickness.
You should know however, that the nasal spray is not recommended for anyone young than 2, older than 49, immunocompromised or between the ages of 2 to 17 who take aspirin-containing medications.
A high-dose vaccine is also available for adults older than 65, and research suggests it is more effective in preventing flu in elderly adults than the standard flu shot.
Vaccines protect more than just the people who are vaccinated; they prevent the virus from being spread to those who aren't. This is especially important for infants and people with conditions that restrict their ability to get the flu shot. The more people get the flu shot, the greater protection we have against the flu.
The flu shot is just the first step in preventing winter illnesses. Tincher also recommends staying away from sick people when you can. Other infection-reducing steps include:
- Washing your hands regularly with soap and water for at least 20 seconds
- Avoiding touching your nose, eyes and mouth with unclean hands
- Routinely disinfecting objects and surfaces in your home, office and classroom
- Managing stress with techniques like physical activity or calling a friend
- Getting 7 to 9 hours of sleep each night
- Eating a healthy, well-balanced diet
Help keep others flu-free by staying home for at least 24 hours after your fever subsides and covering your mouth when you cough or sneeze.
