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Flu Guide: What to Know This Season

7 Risk Factors That Make Flu More Deadly

What to know if you have heart disease, diabetes, cancer and more

three images picturing health conditions a blood glucose monitor to show diabetes a man using an inhaler to show asthma or lung conditions and a person using a wrist cuff blood pressure monitor for heart conditions

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En español | COVID-19 may be top of mind these days, but health experts warn it’s just as important to guard against the regular seasonal flu this year — especially if you’re in a group that’s at higher risk for severe or deadly complications.

 During the 2019-2020 flu season, influenza caused as many as 740,000 hospitalizations, according to the Centers for Disease Control and Prevention (CDC). Previous flu seasons have been even worse, and 2017-2018 was an especially severe season, causing an estimated 61,000 American deaths.


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There’s no way to know how bad this year’s season will be, but experts are worried about overlap between the flu and COVID-19. Both diseases are especially dangerous to older adults, and they have the potential to overwhelm hospitals trying to treat them simultaneously.

While anyone can have a bad case of flu, certain groups are more likely to experience dangerous complications, ranging from pneumonia and dehydration to heart failure and death. Many of the same groups are also at higher risk from COVID-19.  

The more risk factors you have, the higher your chance of a bad outcome. Here are seven common risk factors, why they put you in danger and what you can do — beyond getting that all-important flu shot to blunt, or eliminate, flu’s worst effects. 

1. Risk factor: You’re age 65 or older 

Older adults are the demographic most affected by both flu and COVID-19. The CDC estimates that 70 to 85 percent of flu-related deaths and up to 70 percent of flu-related hospitalizations occur in people 65 and older.

About half of adults age 65-plus also have a second risk factor that makes them vulnerable, according to National Foundation for Infectious Diseases estimates.

But even healthy older adults are at risk, because “your immune system simply is not as robust as it was when you were 25 years old,” notes William Schaffner, M.D., medical director of the National Foundation for Infectious Diseases and a professor of infectious diseases at Vanderbilt Medical Center in Nashville, Tennessee. 


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In addition, typical flu symptoms don’t always show up in older adults, causing a delay in diagnosis and treatment. 

“The most important symptom that may not be present in older people is fever,” Schaffner says. “People can develop a cough, feel weak, and they may even get confused, but they don’t have a fever, so family members don’t think they have the flu.” 

2. Risk factor: You have heart disease or a history of stroke 

Researchers in recent years have uncovered a concerning link between the flu and heart complications. 

A CDC study published in August, for instance, found that 1 out of 8 older patients hospitalized with flu had a serious cardiac event (and the study looked at a big group of patients, 80,000 overall). Another study, published in 2018, found that you are six times as likely to have a heart attack during the week after being diagnosed with influenza as at other times.  

In both studies, a history of heart disease and stroke boosted the likelihood of a sudden heart complication. Doctors think the flu triggers an inflammatory response in your body, which in turn can create dangerous clotting in your blood vessels. 

“It’s like collateral damage in a war,” Schaffner says. “For up to a month after you recover from the flu, your body’s inflammatory response is still ginned up and having an effect on your body, putting you at increased risk for heart attack and stroke.”  

The flu vaccine is key here. In a recent study, adults over 50 who got flu vaccines during a hospitalization had a 28 percent lower risk of a heart attack over the next year. They also had a 47 percent lower risk of a mini stroke, an 85 percent lower risk of cardiac arrest and a 73 percent lower risk of overall death.

3. Risk factor: You have diabetes

Diabetes weakens your immune system, making it harder for your body to fight off disease, says Joseph Gastaldo, M.D., system director of infectious diseases at OhioHealth in Columbus, Ohio. Influenza can also make it more difficult to control your blood sugar levels: Your levels may rise in response to the infection, or they may fall if you don’t feel like eating while you’re sick. Meanwhile, your symptoms can make it difficult for you to recognize the signs of high or low blood sugar. 

“It’s very easy for diabetics [who get the flu] to become dehydrated or have issues with their kidneys,” Gastaldo says. 

Diabetics are three times as likely as other people to die of flu-related complications, and six times as likely to be hospitalized. The good news is, getting a flu vaccine reduces your risk of hospitalization by up to 79 percent, studies show.  

4. Risk factor: You have a lung disease or asthma

If you have chronic obstructive pulmonary disease (COPD), such as emphysema or chronic bronchitis, the flu can cause your airways to swell and become blocked with mucus, making it harder to breathe. If you have asthma, even if it’s controlled, the virus will likely inflame your airways and trigger asthma attacks. 

Adults with both COPD and asthma are at greater risk of developing pneumonia or another respiratory infection as a result of the flu. You can end up hospitalized or with severe and permanent damage to your lungs.  

Getting the flu vaccine can help. It’s associated with a 38 percent reduction in influenza-related hospitalizations among patients with COPD, according to a 2019 study published in the journal Chest

5. Risk factor: You have a chronic condition or a weak immune system

In addition to things like heart and lung disease, many other conditions increase your chance of a poor outcome from flu. Those include liver disease, kidney disease, blood disorders, metabolic disorders and neurological conditions. 

Some chronic conditions leave you vulnerable because they weaken your immune system or require you to take medicine that does, Gastaldo says. 

“A lot of older adults today take immunosuppressants for conditions such as rheumatoid arthritis or cirrhosis,” Gastaldo says. “And there are more people living with transplants — heart, kidney, bone marrow — who take those types of medications.” 

Immunocompromised patients may not get a fever with the flu, so it’s important to pay attention even to mild symptoms. They are at especially high risk for a secondary infection like pneumonia, according to the CDC. 

6. Risk factor: You’ve had cancer 

Many cancer treatments suppress your immune system, so it may not be surprising that cancer patients are three to five as times likely to be hospitalized for influenza as the general population. 

But studies show you also face a greater risk if you’ve had cancer in the past, especially leukemia or lymphoma. In addition, some types of chemotherapy alter your immune system for the long term, making you more vulnerable to a severe case of the flu. 

If you’re undergoing cancer treatment now, the American Cancer Society recommends talking to your oncologist about the best time to get the flu shot — but do get it. In a 2019 study that analyzed data on more than 26,000 cancer patients, those who got a flu shot were significantly less likely to get the flu and to be hospitalized from the virus. 

7. Risk factor: You are obese 

Anyone with a body mass index greater than 40 is at increased risk of flu complications, according to the CDC, even obese adults who have no other health issues. 

It’s unclear exactly why obesity is a factor, Gastaldo says, but it may be because the vaccine is less effective in overweight people, because obesity itself impairs the immune response or because the extra weight makes it more difficult to take the deep breaths necessary to aerate your lungs. 

Studies show obese people also carry the flu virus for longer and are more likely to spread it to others. 

How to protect yourself if you’re at higher risk

Two vaccines you need, and why this season you shouldn’t hesitate to call a doctor

If you’re in a high-risk group, you can strengthen your immune system by eating healthy, exercising regularly and getting enough sleep. In addition, the precautions most Americans are taking to guard against the coronavirus — handwashing, wearing face coverings and staying 6 feet away from others — will help protect you from the flu. 

But experts agree that the three most important steps you can take to reduce your risk from influenza are these:

Get your annual flu shot. 

Being vaccinated is by far the most effective way to protect yourself from the flu. The vaccine is safe for nearly everyone over 6 months old, and study after study shows that it significantly reduces the risk of flu-related complications, hospitalization and death. Older adults should specifically ask for the high-dose vaccine or one with an ingredient called an adjuvant because they help boost the immune response. 

Get the pneumonia vaccine. 

The most common complication of the flu is pneumonia, and you can help guard against it and other dangerous infections by getting the pneumonia shot. The CDC recommends that all people over 65 get at least one pneumonia vaccine, while those with chronic conditions should get two different pneumonia shots, at least a year apart. 

Contact your doctor at the first sign of symptoms. 

Getting in touch with your medical provider right away is especially important this year, since COVID-19 and the flu share many of the same symptoms. Chances are, your doctor will want to test you right away for both COVID-19 and the flu. 

“We want you to have your antenna up really high for symptoms,” Gastaldo says. “If you have more trouble breathing, less energy, a low-grade fever, shortness of breath or if you’re a diabetic and your blood sugars are all of a sudden very high, don’t wait to call.”

Time is of the essence if you have the flu, Schaffner says, because antiviral medications like Tamiflu are most effective if they’re taken within the first 48 hours. The medications can minimize your risk of complications and shorten the duration of your illness.

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