Why the flu is serious when you have a chronic illness

Every winter brings cold winds, icy pavements and the flu. While the flu is usually mild, for vulnerable groups, it can cause severe illness (1).

The flu can be extremely serious in people with long-term medical conditions (2). Our chronic illnesses mean we’re more likely than others to develop potentially serious complications such as bronchitis and pneumonia – and we could even end up in the hospital (1)  (3).

Let’s explore why our already weakened immune systems are less able to fight off the flu and, indeed, how the flu may make our underlying health conditions worse.

Heart disease

Chronic heart conditions, including heart failure or congenital heart disease, may leave your body too weak to fight off the flu, increasing your risk of experiencing flu-related complications, such as pneumonia (4).

On the other side of the coin, the flu can also make your heart disease worse, increasing your risk of a heart attack or a stroke (4)  (5). Don’t delay getting a medical professional to evaluate any heart symptoms, particularly in the first week of infection (7). The flu can also affect your blood clotting rate (INR) (6), so monitor your blood clotting rate more closely while you’re not feeling well if you take Warfarin.


If you have diabetes, you’re also more at risk of potentially serious flu complications such as pneumonia (8)  (9). Also, your blood glucose levels may rise in response to the infection (9). But equally, not feeling like eating with the flu could cause your blood glucose levels to fall (10). Either way, it’s important to check blood glucose levels more regularly than usual when you have the flu.

But that’s not all. Feeling ill with the flu might mask the symptoms of high or low blood sugar (9), which makes it more difficult for you to manage your diabetes and puts you at even more at risk of serious diabetes complications.

Respiratory diseases

If you have asthma, your chronic condition means your flu may be more severe, even if your asthma is mild or well-controlled (11), because the flu can make your already swollen and sensitive airways more inflamed. The narrowing of your airways could exacerbate your asthma symptoms – and may even trigger an asthma attack (12) and lead to a stay in hospital (13).

Likewise, if you have a chronic obstructive pulmonary disease (COPD), such as emphysema or chronic bronchitis, your flu symptoms are also likely to be more severe (14). You’re also at greater risk than others of developing an infection in your airways (14) since COPD can put a significant strain on your body, making you more vulnerable to infections (15).

Weakened immune system

People with an HIV infection are also at high risk of serious complications if they catch the flu (16) and more likely than others to catch the flu (17). If you are unfortunate enough to catch the flu, compared with others your symptoms are more likely to last for longer (18), your illness is more likely to be severe (17), and you are more likely to be hospitalised (17).

If you have cancer, your cancer treatments – your chemotherapy or radiation – may weaken your immune system, increasing your risk of catching the flu and developing complications (19)  (20). What’s more, if you catch the flu, you might not be able to attend appointments, delaying your treatment (19).

With inflammatory arthritis, doctors may prescribe treatments that suppress your immune system to reduce symptoms (21). However, this suppression can also mean your immune system is less able to fight infections, making you more likely than others to catch flu (21).

You also an increased risk of developing serious infections if you do not have a spleen or have a spleen that does not work properly (22). In fact, anyone with an immune deficiency has a lower resistance to infections (23). Your body will also find it more difficult to cope with infections, leading to unexpected complications. The flu dangerous for you, but it can also make your immunosuppression worse (24).

Liver and kidney disease

Chronic liver disease also puts you at risk from the flu, which could develop into something more serious, such as bronchitis or pneumonia (24). And if you have chronic kidney disease, not only does your body find it much harder to fight off the flu but infections can lead to problems with other organs in your body (25).

You may have had a transplant or be waiting for one. If this is the case, then you’re more at risk of developing complications if you catch the flu (25).  If you are waiting for a transplant and have the flu when an organ becomes available, you may not be well enough to have the operation (25).

Neurological conditions

For those of you who have a chronic neurological disease, the flu can make your symptoms much worse and can lead to problems with different organs in your body (26). Some of these complications can be extremely serious:

  • If your neurological disease affects your lungs and makes breathing difficult, the flu makes breathing even harder and can develop into pneumonia (26).
  • If your neurological disease makes it difficult for you to regulate your body temperature, the flu can cause you to develop a high temperature (26).
  • And if you have Multiple Sclerosis, the flu can make your symptoms worse (26); one-third of people with MS who catch the flu have a relapse within six weeks.

Anyone who finds communication difficult might have problems telling the people who care for them if they start to feel very ill (26), delaying treatment and making symptoms worse.

Whatever your chronic condition, flu vaccination is especially important simply because you’re at high risk of developing serious complications if you catch the flu. What steps have you taken to keep yourself well this winter? Have you had your flu vaccine yet?



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