How the Flu Affects Babies

Knowing when to contact a healthcare provider

The flu (influenza) can usually be managed in adults, teens, and older children, but babies and children under two are at high risk of complications due to their immature immune systems. Because of this, they are more likely to be hospitalized, develop pneumonia, and possibly die as a result of the infection.

Babies under six months are at the highest risk overall because the flu vaccine cannot be used in them safely.

This article will describe the signs and symptoms of flu in babies and toddlers so that you know when it's time to seek immediate medical care. It will also offer tips on how to prevent the flu, including the right time to get a flu shot.

Young toddler girl in bed with the flu
PhotoAlto / Anne-Sophie Bost / Getty Images

What Causes the Flu?

Influenza (flu) is a highly contagious respiratory infection caused by the influenza virus. There are two types: influenza type A and influenza type B. Type A can affect humans and certain animals (such as with bird flu or swine flu), while type B only occurs in humans.

The virus is mainly passed through respiratory droplets created when people with flu cough, sneeze, or talk. The bulk of infections happen during "flu season" (roughly October through March) but can occur any time of the year.

Because the virus has many strains, each of which rapidly mutates, you can get flu year after year and even more than once a year. You are never immune to the virus.

With that said, you can greatly reduce your risk by receiving the annual flu vaccine, which changes every year based on which strains are most likely to dominate. But even with a flu shot, you can still get the flu, although generally less severely.

Why Young Children Are at a Greater Risk

According to the Centers for Disease Control and Prevention (CDC), children under five years of age—and especially those under two—are at higher risk of developing serious flu-related illnesses than older children and adults.

This is because their immune systems have not yet developed a defensive response to the virus in the form of antibodies. Antibodies are proteins produced by the immune system that target disease-causing organisms like the flu virus for destruction.

While no one is ever fully immune to the virus (because it is constantly changing), with every infection your body "remembers" the virus and creates longer-lasting antibodies to trigger a response should it return.

Because babies and toddlers have not developed these defenses, they are more vulnerable to severe infections and potentially life-threatening complications like:

  • Pneumonia: An infection of the air sacs of the lung
  • Encephalopathy: A brain complication caused by persistent high fever
  • Myocarditis: Inflammation of the sac surrounding the heart
  • Severe dehydration: Due to high fevers that deplete the body of water
  • Sepsis: The severe overreaction of the immune system to an infection

On rare occasions, these and other complications can cause death.

Latest Statistics

According to the CDC, between 7,000 and 26,000 children under five are hospitalized each year because of the flu. Many more require care from a healthcare provider, urgent care center, or emergency room. From 2019 to 2020, 199 children died of flu-related complications in the United States.

Flu Signs and Symptoms in Babies

The flu can rapidly turn serious in babies in part because they cannot tell you what they feel. They may be fussy or experience symptoms you assume are related to the common cold. Even among toddlers who can speak, the symptoms are often very different from those in adults.

Call your healthcare provider if your baby has the following signs and symptoms of the flu:

  • Fever over 100 F
  • Frequent cough
  • Runny or stuffy nose
  • Persistent fatigue (tiredness)
  • Vomiting or diarrhea
  • Difficulty feeding or refusing to drink
  • Persistent fussiness and unwillingness to play or smile

Even if you're not sure what you are dealing with, it's best to play it safe and speak with a healthcare provider. If they are not available, try a telehealth service or a walk-in clinic near you.

When to Go to an Emergency Room

If your child has the flu, it is important to recognize the signs and symptoms of a medical emergency. Call 911 or rush to the nearest emergency department if your child experiences:

  • Shortness of breath or wheezing
  • Severe lethargy or difficulty waking up
  • Persistent vomiting
  • Severe diarrhea
  • Lack of tears with crying
  • Lack of urination or wet diapers for eight hours
  • Blue lips or skin
  • Fever over 100 F for infants three months or younger
  • Return of fever and flu symptoms after they've gone away
  • Seizures or convulsions

Diagnosis and Treatment

The diagnosis of flu in babies and toddlers is based on observation and a review of the child's symptoms. Nothing else is needed to confirm the diagnosis.

Other tests may be ordered if there are signs of complications such as pneumonia, encephalopathy, myocarditis, or sepsis, These may include blood tests, X-ray or other imaging studies, or electrocardiogram (ECG) to measure the electrical activity of the heart.

Your healthcare may prescribe antiviral medications that can shorten the length and severity of the flu (and may even help prevent pneumonia). These are most effective when started within two days of the first signs of the flu.

In the United States, there are three antivirals approved for use in treating flu in children:

What Parents Can Do to Prevent the Flu

Preventing the flu in children is a far better option than treating it. Central to this is annual flu vaccination starting at six months of age.

There are two flu vaccine options currently available for children:

  • Flu shots: Delivered by injection into the upper arm or thigh and approved for children six months and over
  • FluMist: An inhaled nasal vaccine approved for children two years and over

The CDC recommends that children receive the vaccine every year around the end of October. Children between the ages of six months and eight years should get two doses if they have not been vaccinated before. Thereafter, they only need one dose.

Flu Prevention in Newborns

Babies under six months cannot get the flu shot. This is because their immune systems are too underdeveloped and may react adversely to the vaccine.

However, there are still several ways to protect them from the flu:

  • Maternal vaccination: People who are pregnant during flu season should get the flu shot before their baby is born. The flu vaccine is safe during pregnancy and has been shown to protect the baby from the flu for up to six months after birth.
  • Breastfeeding: Breast milk contains antibodies that help strengthen your baby's immune system. This includes antibodies produced in response to the flu vaccine.

Flu Prevention Tips

In addition to the flu shot, the following precautions can help protect your baby from getting the flu:

  • Wash your hands frequently.
  • Keep your baby away from sick people.
  • Be sure that everyone who cares for your baby is vaccinated.
  • Cover your cough with your elbow or a tissue.

Summary

Children under five years of age, and especially those under two, are at increased risk of complications from the flu (influenza), including pneumonia, myocarditis, and sepsis. To avoid this, it is important to recognize the signs and symptoms in babies and young children, including fatigue, fever, cough, poor feeding, persistent fussiness, vomiting, and diarrhea.

You can help prevent the flu by getting your child vaccinated every year starting at six months of age. Children six months and over can get the flu shot. Those two years and over can receive the nasal flu vaccine.

A Word From Verywell

Severe illnesses and rare cases of death from flu mainly occur in unvaccinated children. Despite what some people may tell you, the flu vaccine is safe and is in no way linked to autism, ADHD, or any other medical condition.

When it comes to babies and toddlers who have not yet developed the immune defenses to avoid severe infections, the benefits of annual flu shots far outweigh any risks, real or presumed.

Frequently Asked Questions

  • How long does it take flu symptoms to show in babies?

    The incubation period for the influenza virus (meaning the time from exposure to the appearance of symptoms) is anywhere from one to four days in babies.

  • How long will flu symptoms in babies last?

    if your baby or toddler comes down with the flu (influenza), you can expect symptoms to last for around a week and sometimes up to two. With that said, there may be a lingering cough for up to four weeks.

  • When do flu symptoms peak in babies?

    Symptoms of the flu (influenza) tend to be at their worse two to four days after the onset of symptoms. Thereafter, they tend to rapidly wane and generally resolve within a week.

11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Centers for Disease Control and Prevention. Understanding influenza viruses.

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  5. Centers for Disease Control and Prevention. Flu symptoms & complications.

  6. Centers for Disease Control and Prevention. Pediatric flu deaths during 2019-2020 reach new high.

  7. Bhat YR. Influenza B infections in children: a review. World J Clin Pediatr. 2020 Nov 19;9(3):44–52. doi:10.5409/wjcp.v9.i3.44

  8. MedlinePlus. Your baby and the flu.

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By Kristina Duda, RN
Kristina Duda, BSN, RN, CPN, has been working in healthcare since 2002. She specializes in pediatrics and disease and infection prevention.