For most people, the flu represents a few days of feeling miserable. Body aches, fever, cough, runny nose, sore throat, chills, and fatigue are common symptoms.

Adults may call in sick to work to stay home and rest. Young children may need to take a couple days off of school.

But for certain populations, including very young children and older adults, the flu can be more dangerous. In some cases, the flu is a contributor to death, even if it’s not the main cause.

Vaccinations and better education about hygiene and public safety help reduce the number of flu infections each year. But influenza can affect anyone of any age group.

Certain populations are more at risk for serious health complications from the flu:

  • children under the age of five, especially those two years and younger
  • children 18 and under who take aspirin or medications that contain salicylate
  • American Indian and Native Alaskan people
  • adults ages 65 years and older
  • pregnant women
  • people with serious medical conditions
  • people taking immunosuppressive agents (e.g., chemotherapy)
  • people with severe obesity

People at increased risk may be interested in the CDC’s “FluView,” a weekly surveillance report that tracks how the flu is affecting various populations throughout the nation. Discovering how prevalent the virus is in your area may help encourage early vaccination.

Most of these populations are more at risk because their immune systems are compromised.

Children

Children’s immune systems are still developing. The CDC reports that about 20,000 children under the age of five are hospitalized for flu-related complications each year.

During the 2009 swine flu epidemic, children ages 5 to 14 were 14 times more likely to be infected than adults over 60 years old.

Seniors

Seniors are more likely to have immune systems that may not be able to effectively fight off infection.

Pregnant women

Expecting moms experience changes to the immune system, heart, and lungs. This makes them more vulnerable to severe illness.

Medical conditions

The flu can weaken the body’s strength and increase inflammation, making preexisting medical conditions worse. These may include chronic lung disease, heart disease, and blood disorders.

Other conditions that can increase the risk of complications include kidney disorders, asthma, epilepsy and other neurological conditions, and diabetes.

Anyone with a weakened immune system caused by diseases is also in this group. This includes people living with diabetes, HIV, and cancer.

Obesity

Obesity compromises the immune system response. A 2010 study published in the journal PLOS One found that morbid obesity was associated with hospitalization and death due to the H1N1 swine flu infection.

Typical symptoms of the flu include:

  • fever
  • cold chills
  • malaise
  • runny or stuffy nose
  • cough
  • sore throat
  • muscle and body aches
  • headaches
  • tiredness
  • vomiting
  • diarrhea

Populations at risk for more serious effects may experience the following complications.

Ear infections

Children are especially at risk for ear infections. These may develop because of inflammation in the throat and inner ear caused by the flu virus.

The virus may also attack the inner ear directly. Children with runny noses, sneezing, and coughing often have fluid buildup in the ear. This can provide the perfect environment for bacterial infections.

Sinusitis

Like ear infections, sinus infections can develop because of the flu. The virus may attack the sinuses directly, or indirectly cause the infection.

The flu creates inflammation and fluid buildup in the sinuses. This can allow other germs to enter and cause sinus infections.

Worsening asthma

People with asthma may experience worsening symptoms when they have the flu. The virus causes inflammation of your airways, and leads to an increased sensitivity to allergens and other asthma triggers.

Pneumonia

The flu is a common cause of pneumonia. Pneumonia with the flu can be deadly. It can cause fluid buildup and reduce oxygen supply to the lungs and other tissues in the body.

Seizures

Children are more often at risk for seizures with the flu. A study from the University of Utah found that the swine flu caused more neurological complications in children than the seasonal flu.

Children who have the seasonal flu with a fever can also have a “febrile seizure.” This type of seizure is characterized by convulsions or rapid twitching or jerking movements.

This is common with body temperatures of 102°F or higher. Febrile seizures usually last only a minute or two. They usually do not cause permanent damage.

Premature labor and delivery

Pregnant women who get the flu are at risk for severe illness and other complications. Respiratory infections, especially those that can cause pneumonia, are linked with low birth weight. They’re also linked with higher rates of preterm birth.

The flu can also be harmful to the developing baby. A 2012 study found that mothers who had the flu with fever were more likely to give birth to children with defects of the brain and spine.

The CDC recommends that pregnant women get a flu shot to protect both the mother and the baby from the flu.

Death

The number of deaths caused by the flu and flu-related complications each year fluctuates with the length and severity of each flu season. However, the disease claims thousands of lives each year.

The CDC reports that an estimated 90 percent of seasonal flu-related deaths in the United States each year occur in people ages 65 years and older.

How do you know when to seek emergency care for the flu? There are several signs that you need to see your doctor immediately. These signs include:

  • difficulty breathing
  • lasting high fever that does not come down with medications
  • skin color that appears bluish or gray
  • dehydration (signs in children include decreased energy, decreased amount of urine in diapers, or lack of tears when crying)
  • pain or pressure in the chest or abdomen
  • sudden dizziness
  • mental confusion
  • severe or persistent vomiting
  • seizures
  • babies that seem listless or lethargic, irritable, or don’t want to eat

Every year, manufacturers develop a vaccine to prevent against the virus strains likely circulating in the upcoming flu season. The CDC recommends that everyone six months and older be vaccinated.

Vaccination is even more important for populations at high risk. These people are protecting themselves not only from the flu, but from more serious complications that can lead to hospitalization. In some cases, flu complications can even cause death.

The exceptions include those who have severe allergies to chicken and eggs, and those who have had reactions to the vaccine in the past. Also, people who are currently ill and have a fever should wait until they feel better to get vaccinated.