Seasonal flu is a viral infection that tends to start spreading in the fall and hits its peak during the winter months. It can continue into the springtime — even into May — and tends to dissipate in the summer months. While most cases of the flu resolve on their own, it can become life-threatening if complications like pneumonia arise alongside it.

The Centers for Disease Control and Prevention estimate that there were between 12,000 and 56,000 flu-related deaths in the United States between 2011 and 2013. However, it’s difficult to accurately track how many cases of the flu each year lead to death from complications. States aren’t required to report flu diagnoses in adults to the CDC, so it’s likely that adult deaths associated with flu go under-reported. What’s more, adults don’t often get tested for flu when they’re sick, but instead get diagnosed with an associated condition.

People often mistake the flu for a bad cold, since flu symptoms mimic a cold. When you catch the flu, you might experience coughing, sneezing, runny nose, hoarse voice, and a sore throat. But flu can progress into other conditions like pneumonia, chronic obstructive pulmonary disease (COPD), and congestive heart failure, which can quickly become life-threatening.

Flu can directly lead to death when the virus triggers severe inflammation in the lungs. When this happens, it can cause rapid respiratory failure because your lungs can’t transport enough oxygen into the rest of your body. The flu can also cause your brain, heart, or muscles to become inflamed. This can lead to sepsis, an emergency condition that can be fatal if not immediately treated.

If you develop a secondary infection while you have the flu, that can also cause your organs to fail. The bacteria from that infection can get into your bloodstream and cause sepsis, as well.

In adults, symptoms of life-threatening flu complications include:

  • feeling short of breath
  • trouble breathing
  • disorientation
  • feeling suddenly dizzy
  • abdominal pain that is severe
  • pain in the chest
  • severe or ongoing vomiting

Life-threatening symptoms in babies include:

  • temperature higher than 100.3˚F (38˚C) in babies 3 months or younger
  • reduced urine output (not wetting as many diapers)
  • inability to eat
  • inability to produce tears

Emergency flu symptoms in small children include:

  • irritability and refusing to be held
  • inability to drink enough, leading to dehydration
  • breathing rapidly
  • stiffness or pain in the neck
  • headache that isn’t alleviated with over-the-counter pain relievers
  • trouble breathing
  • a blue tinge to the skin, chest, or face
  • inability to interact
  • difficulty waking up

People with compromised immune systems are at risk of developing complications — and possibly dying — from the flu. When your immune system is weakened, you’re more likely to experience viruses and infections in a more severe form. And your body will have a harder time not only fighting those off, but also fighting any subsequent infections that could develop.

For example, if you already have asthma, diabetes, an autoimmune disorder, lung disease, or cancer, getting the flu could cause those conditions to get worse. If you have a kidney condition, getting dehydrated from the flu could worsen your kidney function.

Babies, young kids under age 5, and adults 65 and over are at the highest risk of developing severe complications from the flu, being hospitalized, and dying. Other people at high risk of dying from flu include:

  • women who are pregnant or are less than two weeks postpartum
  • anyone who experiences chronic illness
  • people who have compromised immune systems
  • people living in long-term care, assisted living facilities, or nursing homes
  • people who have a BMI of 40 or over
  • organ donor recipients who take anti-rejection drugs
  • people living in close quarters (like members of the military)
  • people with HIV or AIDS

Adults over 65, including the elderly, are more likely to have chronic illness or compromised immune systems and tend to be more susceptible to infections like pneumonia. On the other hand, children tend to be more likely to have an immune over-response to flu strains they haven’t been exposed to before.

People who are sick with the flu can lower their chances of developing complications by being extra vigilant of the symptoms they’re experiencing. For example, feeling short of breath isn’t a normal symptom of the flu.

If you have the flu and continue to get worse instead of better, that’s a good indication it’s time to see your doctor. Flu symptoms should only last a week, and you should be able to alleviate them through treatment at home. Taking over-the-counter medications for fever, body aches, and congestion should be effective. However, that’s not always the case.

While most viruses run their course on their own, you shouldn’t try to wait out symptoms that get more and more severe. Full recovery from flu sometimes requires medical attention, as well as plenty of fluids and rest. If flu is diagnosed early enough, your doctor can also prescribe antiviral medication that shortens the duration of your symptoms.

While the flu usually isn’t life-threatening, it’s better to be on the safe side. You can take measures to protect yourself against the flu, like thoroughly washing your hands with warm, soapy water. Avoid touching your mouth, eyes, or nose, especially when you’ve been out in public during flu season.

Your best chance at preventing the flu is by getting a flu vaccine every year, at any time during flu season. Some years it’s more effective than others, but it never hurts to have an extra layer of protection against what proves to be a life-threatening illness for thousands of people every year. Every year, up to four strains are included in the vaccine.

Getting the flu vaccine also helps protect the people you love from catching the flu from you. While you might be healthy, you could catch flu and unwittingly pass it on to an immunocompromised, elderly, or very young person.

The CDC recommends flu vaccines for everyone older than 6 months. Right now, the injectable form of the vaccine is the only kind available.