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What is flu?

Seasonal flu (also known as influenza) is a highly infectious illness caused by the flu virus.

The virus infects your lungs and upper airways, causing a sudden high temperature and general aches and pains, headache, weakness and exhaustion. Symptoms can last for up to one week. You may need to stay in bed until your symptoms get better. Flu affects people of all ages. In some people flu can cause serious complications such as pneumonia.

Flu is serious

The Flu virus is an unpredictable virus.

If you are healthy you will usually recover in 7 days. But Flu can be severe and can cause serious illness and death.

Complications of flu include bronchitis, pneumonia, ear infections and rarely acute encephalopathy (swelling of the brain).

Serious complications of flu are more likely if you have a chronic medical condition or if you are aged 65 years or older. Pregnant women are also at increased risk of flu complications.

In Ireland, between 200 and 500 people, mainly older people, die from flu each winter.

Every year, around the world, flu causes between 3 and 5 million cases of severe disease and up to 646, 000 deaths.

The difference between a cold and the flu

Flu symptoms come on suddenly with a fever, muscle aches, headache and fatigue. A cold usually starts gradually with a sore throat and a blocked or a runny nose. Symptoms of a cold are generally mild compared to flu.

Compare symptoms of COVID-19, flu and cold

Symptoms

COVID-19

Seasonal flu

Cold

Symptoms range
from mild to severe

Abrupt onset
of symptoms

Gradual onset
of symptoms

Fever or chills

Common

Common

Rare

Cough

Common (usually dry)

Common (usually dry)

Mild

Shortness of breath

Common

No

No

Lost or changed sense
of smell or taste

Common

Rare

Rare

Fatigue

Common

Common

Sometimes

Aches and pains

Common

Common

Common

Sore throat

Sometimes

Sometimes

Common

Headaches

Sometimes

Common

Rare

Runny or stuffy nose

Sometimes

Sometimes

Common

Feeling sick or 
vomiting

Rare

Sometimes

No

Diarrhoea

Rare

Sometimes in children

No

Sneezing

No

No 

Common

How flu is spread

If you are carrying the virus, you can spread it by coughing or sneezing. This can happen from 1-2 days before symptoms develop and up to 5 days after symptoms develop.

Flu can survive on worktops and objects, especially in low temperatures and low humidity. You can get flu by touching a surface with the virus on it and then touching your mouth, eyes or nose. The virus can live on a hard surface for up to 24 hours and a soft surface for around 20 minutes.

More information

 


Getting the flu vaccine is a safe and effective way to help prevent flu, avoid hospitalisation and reduce flu-related illness and death.

Some people are more at risk of getting complications if they catch flu.

You can get the flu vaccine for free if you:

  • are 65 years of age and over
  • are pregnant
  • are a child aged 2 to 12 years (new for 2020/2021)
  • are an adult or child aged 6 months or older with a long-term health condition like
    • chronic heart disease, including acute coronary syndrome
    • chronic liver disease
    • chronic renal failure
    • chronic respiratory disease, including chronic obstructive pulmonary disease (COPD), cystic fibrosis, moderate or severe asthma or bronchopulmonary dysplasia
    • chronic neurological disease including multiple sclerosis, hereditary and degenerative disorders of the central nervous system
      diabetes mellitus
    • haemoglobinopathies
    • morbid obesity i.e. body mass index (BMI) over 40
    • immunosuppression due to disease or treatment (including treatment for cancer)
    • are a child with a moderate to severe neurodevelopmental disorder such as cerebral palsy
  • were born with Down syndrome
  • live in a nursing home or other long-term care facility

Some people should get the vaccine to protect themselves, their families and those they care for.

These include those who:

  • work in healthcare
  • are a carer or live with someone who is at risk of flu because of a long-term health condition
  • are a carer or live with someone who has Down syndrome

People who are in regular contact with pigs, poultry or waterfowl should get the flu vaccine. 

If you are in an at-risk group, you should get the flu vaccine as early into the flu season as you can.

You should recover at home within a week, without needing medical care. Contact your GP if you have severe symptoms or if you are aged 65 years and older, are pregnant, or if you have a long-term health condition that puts you at risk of complications of flu.


If you are at home with flu or taking care of someone at home, follow these tips to help stop the flu spreading:

  • If you have the flu stay in one room with the door closed and, if possible, a window open
  • Family members should limit time spent with someone with flu and avoid sharing dishes, books, toys, etc
  • Avoid face-to-face contact with someone who has the flu
  • Discourage visits from people not living in the house
  • If you have flu, cover your nose and mouth with disposable tissues when sneezing or coughing. If tissues are not available, coughing or sneezing into your arm or sleeve (not hand) is recommended
  • Used tissues should be put into a bin and the bin sealed in the room and immediately taken outside for collection
  • Wash hands often with soap and water or alcohol-based hand rub, especially after coughing and sneezing
  • Everyone in the house should frequently clean their hands with soap and water or an alcohol-based hand rub, especially after every contact with someone with flu or their room or bathroom
  • Avoid touching the eyes, nose and mouth with your hands as this helps spreads the flu virus
  • Surfaces and items inside the house should be cleaned regularly with bleach-based household cleaners

The flu is responsible for 200-500 deaths each year in Ireland. In a severe season it maycause up to 1,000 deaths.

  • Flu can cause serious complications such as pneumonia, especially in those aged 65 and older, pregnant women and children and adults with long-term medical conditions
  • An increase in flu cases leads to an increase in heart attacks and strokes
  • Flu can cause serious disease in previously healthy people
  • Every year, hundreds of people are hospitalised with flu. In 2019/2020, which was a moderate flu season, more than 4332 people were hospitalised with flu and 154 people admitted to critical care (intensive care) units.
  • It is easy to pass on the flu and anyone infected can spread the disease from 1 day before symptoms begin (asymptomatic) and for 3 to 5 days after developing symptoms
  • Flu occurs every winter but it is not possible to know whether there will be a mild or a severe season in each year

Antiviral medicines like Tamiflu and Relenza are used to treat the symptoms of flu and to try to reduce the severity. They are only required for people whose symptoms are severe, or for people in the risk groups who develop the flu. The GP will decide on whether a person needs antiviral medicine or not.

Facts about flu