Influenza (Flu): Who Is At Risk For Severe Illness?

Parents with young kids

Different reactions to flu

Influenza (the flu) can create different reactions in people:

  • Some people will get mildly sick. They may take a few days off work or school. They may visit the doctor. They may take pain relievers or other medications. They will recover after a few days.
  • Some people will get very sick. They may need to stay in a hospital. They may be given antiviral medications and antibiotics. They may need intensive care.

Who gets​ very sick from the flu?

The vast majority of people with the flu will get mildly sick. The groups who may get very sick are:

  • the very young (younger than two, but children up to six years old may still become very sick)
  • the elderly (older than 65)
  • people who have underlying health conditions or are already sick with something else

Healthy people rarely require hospitalization or get very sick from the flu. 

​Children at high risk 

Children with weak immune systems 

Children with weak immune systems will have a harder time fighting off illness. These children may also have problems taking medications for infections. Children can have weak immune systems for different reasons, including:

  • receiving an organ transplant
  • receiving a bone marrow transplant
  • congenital immunodeficiency
  • some nutritional deficiencies
  • severe burns
  • taking immunomodulators and immunosuppressive agents
  • being on long-term steroid therapy

Some medical conditions can also put children at high risk

Chronic health conditions, severe enough to require regular medical follow-up, can put children at high risk of getting very sick from the flu. These include:

  • heart and lung disorders, including chronic asthma
  • diabetes and other metabolic diseases
  • cancer, immune deficiency and immune suppression
  • kidney disease
  • anemia or other blood conditions such as sickle cell disease and thalassemia
  • cystic fibrosis and other conditions that affect lung secretions
  • conditions treated for long periods with ASA (acetylsalicylic acid or Aspirin)
  • epilepsy
  • cerebral palsy
  • other neurological disorders, including intellectual disabilities or developmental delays
  • obesity


What measures can parents of high-risk children take?

Parents of children with weak immune systems over the age of six months or with chronic (long-lasting) conditions should speak with their doctor about getting the flu shot. It is rare for the flu shot to be not recommended. To avoid getting the flu and passing it to their child, parents and family members of children with weak immune systems or chronic conditions, regardless of whether the child received the flu shot, should also get the flu shot. For tips on making vaccinations as easy and pain-free as possible, read the articles, Pain-free injections in babies and Pain-free injections in children over 1 year of age.

Pregnant women are at ​risk

Women who are pregnant should get the flu shot to protect themselves and their newborn infant

Key poi​nts

  • Very young children or children with a pre-existing condition are at high risk of developing a severe form of flu.
  • The best way to avoid getting the flu is to get the flu shot, keep away from infected people, regularly wash your hands and keep surfaces people regularly touch clean.​

Upton Allen, MBBS, MSc, FRCPC, FAAP

Shawna Silver, MD, FRCPC, FAAP, PEng​


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Seasonal Influenza (Flu) (2013, April 8). Health Canada. Retrieved December 20, 2013.

Key Facts about Influenza (Flu) & Flu Vaccine. (2013, September 26). Centers for Disease Control and Prevention. Retrieved December 20, 2013.

Protect yourself, your family and your community. (2013, October 31). Ministry of Health and Long-Term Care. Retrieved December 20, 2013.

Dominguez-Cherit, G., Lapinsky, S.E., Macias, A.E., et al. (2009). Critically Ill Patients With 2009 Influenza A(H1N1) in Mexico. Journal of the American Medical Association, 302(17):1880-1887.

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