For most people, the flu represents a few days of feeling miserable. Bodyaches, 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.

For certain populations, however, including very young children and the elderly, the flu can be more dangerous. In even more cases, the flu is a contributor to death, even if it's not the main cause.

Influenza Pandemic of 1918

While vaccines and advances in modern medicine have greatly reduced the number of deaths caused by flu each year, the influenza virus caused one of the deadliest epidemics in recorded history. Near the end of World War I, a devastating flu circled the globe, affecting large populations across all age groups. According to the U.S. Department of Health and Human Services (DHHS), the pandemic occurred in three waves over the spring, fall, and winter of 1918, appearing in American port cities as well as parts of Europe and Africa. 

The exact cause is still unknown. Most researchers believe that the influx of returning soldiers may be responsible for the rapid transmission of the virus. Additionally, confusing or absent public health information meant that many people did not take necessary precautions for preventing the spread of the virus. As the flu spread, businesses were shuttered, buildings and homes were quarantined, and entire families were lost to the virus. The pandemic had effectively ended by the summer of 1919. By that time it had claimed the lives of 675,000 Americans, and 20 million people worldwide.

Who Is Most at Risk?

Vaccinations and better education regarding hygiene and public safety help reduce the number of flu infections each year. However, influenza can affect anyone of any age group. Certain populations are more at risk for serious health complications:

  • children under the age of five, especially those two years and younger
  • adults 65 years of age and older
  • pregnant women
  • people with serious medical conditions
  • individuals on immunosuppressive agents (e.g. chemotherapy)
  • people who are morbidly obese 

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.

What Makes Certain Populations More Vulnerable?

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


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 5-14 were 14 times more likely to be infected than adults over 60 years old.


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 sap the body's strength and increase inflammation, making pre-existing medical conditions worse. These may include chronic lung disease, heart disease, and blood disorders (like sickle cell disease). Kidney disorders, asthma, epilepsy and other neurological conditions, and diabetes can also increase risk. Anyone with a weakened immune system due to diseases (such as diabetes, AIDS, or cancer) is also in this group.


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.

What Are Flu-Related Complications?

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.


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 create the perfect environment for 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.


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


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 suffer the seasonal flu with a fever can also suffer a "febrile seizure," which is characterized by convulsions or rapid twitching or jerking movements. This is common with body temperatures of 102 degrees Fahrenheit 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 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. A 2012 study found that mothers who suffered the flu with fever were more likely to give birth to children with neural tube birth defects (defects of the brain and spine).

According to a 2009 study, pregnant women who catch the flu are at risk for flu-related complications, including 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 U.S. each year occur in people 65 years and older.

When to Seek Emergency Care

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 seem listless or lethargic, irritable, or don't want to eat

Can the Flu Be Prevented?

Every year, manufacturers develop a vaccine to prevent against the virus strains likely be 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 individuals are protecting themselves not only from the flu, but from even more serious complications that can lead to hospitalization and 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 should wait until they feel better to get vaccinated.