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Nov 4, 2021

Cold & Flu

Cold & FluFlu SeasonInfluenza

How Flu affects High-Risk Groups

Influenza (commonly referred to as flu) is a viral infection that causes respiratory illness affecting the nose, throat and lungs. On average, ~8% of the US population gets sick from flu each year.

How the Flu is Spread

Contagious viral particles are primarily spread by tiny droplets made when people cough, sneeze or talk. These droplets can land in the mouth or nose of other nearby people and get them sick. A less common way of contracting the virus is by touching a contaminated surface or object that has virus on it and then touching your mouth, nose or eyes.

Common Flu Symptoms

The flu is different from the common cold as the symptoms usually come on suddenly. People who have the flu will often experience some or all of the following:

  • Fever/chills
  • Cough
  • Runny an/or stuffy nose
  • Muscle aches
  • Headache
  • Sore throat
  • Tiredness and fatigue
  • Vomiting and/or diarrhea; although this is more common in children than in adults.

Importantly, not everyone with the flu will have all of these symptoms, including a fever.

Most people who contract the flu will eventually recover in a few days, but some people will develop more serious complications and some of these can be life threatening. Complications of flu can include bacterial pneumonia, ear infections and a worsening of chronic medical conditions such as congestive heart failure, asthma or diabetes.

Who Is at Highest Risk?

Those who are at the highest risk of developing serious flu complications include:

  • Elderly (aged 65 years and older)
  • Children (younger than 5 years)
  • People with certain health conditions

The CDC estimates that from October 1, 2019-April 4, 2020, approximately 39 million—56 million people developed the flu, 410,000–740,000 people were hospitalized due to flu and 24,000–62,000 people died from flu.

Elderly (aged 65 years and older)

People aged 65 years and older have the greatest prevalence of severe flu-related complications due to changes in their immune defenses. It’s estimated that between 70-85% of seasonal flu-related deaths occur in this patient population. Flu-related hospitalizations among this age group contribute to roughly 50-70% or all flu-related hospitalizations each flu season.

Everyday preventative actions should be taken to protect yourself from getting the flu include avoiding people who are sick, covering your coughs and washing your hands often.


Children younger than 5 years old and especially younger than 2 years old are at a higher risk of developing serious flu-related complications and commonly need medical care. Some serious complications that children experience include, pneumonia, dehydration, brain dysfunction, sinus problems, ear infections and sometimes even death. During the 2019-2020 flu season 199 deaths were reported in children due to the flu.

Chronic Health Conditions

In recent flu seasons, 9 out of 10 people hospitalized with the flu had at least one underlying health condition. A flu infection in individuals with the following chronic health conditions can increase their risk of complications:

  • Asthma: Even if you only have mild asthma or your symptoms are well controlled, you are still at high risk of developing serious flu complications. People with asthma can develop swollen airways and inflammation of the lungs. The flu can also cause pneumonia and other respiratory diseases. Asthma is the most common medical condition among children and adults hospitalized with the flu.
  • Heart disease: Heart disease is the most common chronic condition among adults hospitalized with the flu, occurring in roughly 50% of adult patients. A flu infection can increase your risk of having a heart attack by close to 6 times. Sudden, serious heart complications occur in 1 out of every 8 patients (12%) hospitalized from the flu.
  • Diabetes: Even when well managed, people with diabetes are at higher risk of flu complications which can frequently result in hospitalization and sometimes even death. Approximately 30% of adults hospitalized with flu had diabetes in recent years. The flu worsens chronic health problems like diabetes because these conditions can make the immune system less able to fight off infections. Having the flu can also raise your blood sugar levels making them harder to control. Flu vaccinations have been associated with reduced hospitalizations among people with diabetes by 79%.
  • Chronic Kidney Disease (CKD): As CKD weakens the immune response and makes the immune system less able to fight infections, flu infections in this population are correlated with complications such as hospitalization and death. People with CKD at any stage, who have had a heart transplant, or who are undergoing dialysis are all at increased risk of severe illness from the flu.

If you are in any of these high-risk categories and suspect you have the flu, call your healthcare provider immediately. There are antiviral drugs available that can treat the flu and prevent serious complications but they are most effective when used within the first 24-48 hours of symptom onset.

Why We Need to Get Vaccinated Every Year

Every year there are new strains of the flu virus in circulation. Flu viruses have proteins on their surfaces that can differ from year to year through small changes in their DNA. Additionally, flu viruses can interact with other, different types of flu viruses and share their DNA with one another. This can give rise to a completely new type of flu virus that has never been seen by our population. While these types of changes are less common, they do happen and can sometimes cause pandemics. Notable examples include the “Spanish Flu” pandemic in 1918 and the more recent “Swine Flu” pandemic in 2009.

Flu shot

Each year, scientists work on identifying the most common circulating flu viruses and create a new formula of the vaccine that specifically targets these versions. This is why it is important to get vaccinated on a yearly basis, as the targets of the vaccine change every year.

Influenza vaccines can also be cost effective for all ages. In people aged 65 years and older, vaccination has been shown to lower healthcare costs by directly reducing hospitalizations and death. In adults younger that 65 years of age, flu vaccination can reduce both direct medical costs and indirect costs like being absent from work due to illness.

Flu Vaccines Are Life Saving

It is important for everyone eligible to get the flu vaccine every year to protect themselves from illness. For anyone in the above high-risk groups it is especially important to get the vaccine as it has been shown to reduce the risk of serious flu outcomes such as hospitalizations, being admitted to the intensive care unit (ICU) and even death.

This data was informed by:
2 Influenza and Cardiovascular Disease paper

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