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7 Risk Factors That Make Flu More Deadly

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

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COVID-19 may still be top of mind — along with other virus-caused illnesses that are popping up, like monkeypox and polio — 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.

A big reason: Experts worry the flu season could be worse than normal this year, based on trends in the Southern Hemisphere. 

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“We always look to the Southern Hemisphere because they have winter during our summer, and Australia had a very substantial influenza season,” says William Schaffner, M.D., medical director of the National Foundation for Infectious Diseases and a professor of infectious diseases at the Vanderbilt University School of Medicine in Nashville, Tennessee. “There is not always a 1-to-1 correlation, but I’m concerned.” 

And while anyone can have a bad bout of flu, certain groups are more likely to experience dangerous complications, ranging from pneumonia and dehydration to heart failure and death.

Here are seven common factors that put you at risk for a severe case of flu, 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 Centers for Disease Control and Prevention 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,” Schaffner says.

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 2020, 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. 

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“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 a flu vaccine 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 medical director of infectious diseases at OhioHealth in Columbus. Influenza can also make it more difficult to control your blood sugar levels: They 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 to even 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 the immune system, so it may not be surprising that cancer patients are three to five times as 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 have obesity

Anyone with a body mass index (or BMI) greater than 40 is at increased risk of flu complications, according to the CDC, even adults with obesity 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 people with excess weight, 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 people with obesity also carry the flu virus for longer and are more likely to spread it to others.

Editor’s note: This article was published on Oct. 19, 2020. It was updated in October 2022 with new information about the 2022-2023 flu season.

How to protect yourself from flu 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 you have practiced for two years to guard against the coronavirus — handwashing, wearing a mask 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 show that it significantly reduces the risk of flu-related complications, hospitalization and death. This year, the CDC says 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. And the best time to get the shot is September or October, the CDC says. 

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 the pneumonia vaccine.

Contact your doctor at the first sign of symptoms. 

Getting in touch with your medical provider right away is especially important because COVID-19 and the flu share many of the same symptoms, so your doctor may want to test you to see which illness you have. The good news: Both diseases can be treated with antiviral medications that can keep your symptoms from progressing to a more severe state. However, these drugs are most effective if they are taken shortly after symptom onset.  

“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.”

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