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.

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.

How flu is spread

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

This page was updated on 24 August 2021

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 17 years 
  • 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
  • only household contacts or carers of people who have an underlying chronic health condition or have Down syndrome are eligible to receive an influenza vaccine. A carer is described as someone who is providing an ongoing significant level of care to a person who is in need of care in the home due to illness or disability or frailty e.g. those in receipt of a carer's allowance.
    • household contacts of people aged 65 years and older (who do not also have a chronic health condition), pregnant women, children aged 2-17 years or of healthcare workers or carers are not recommended the influenza vaccine.

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.

It may be difficult to tell the symptoms of flu apart from the symptoms of COVID-19. If you have symptoms of COVID-19, you should self-isolate and get a test.

If you are in doubt about any symptoms you have, phone your GP. They will discuss your symptoms with you and advise you on any steps you may need to take.


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 may cause 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. 
  • 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