Vaccine - Flu

The seasonal flu vaccine (flu jab) protects against several strains of flu virus. These are the strains most likely to be circulating this flu season.

The vaccine is available every year to adults and children at risk of flu and its complications.

You need to get a new vaccine each year. This is because the strains of the virus change. This is why it is called seasonal flu. But people commonly call it flu.

You should get your flu vaccine from early October to be covered for flu season.

Flu season usually runs from September to March.

At-risk groups

Some groups of people are more at risk of getting complications if they catch flu. Because of this, these 'at-risk groups' are strongly recommended to get the flu vaccine.

You can get the flu vaccine for free if you're in an at-risk group. 

You are in an at-risk group if you:

  • are a child aged 2 to 12
  • are 65 years of age and over
  • are pregnant
  • live in a nursing home or other long-term care facility
  • have a long-term medical condition – for example, a heart, lung, kidney or neurological disease or cancer
  • have a weak immune system – for example, if you have diabetes or you're having chemotherapy
  • are a child with a moderate to severe neurodevelopmental disorder such as cerebral palsy
  • are obese who have a body mass index (BMI) of over 40
  • were born with Down syndrome

Read more about flu vaccine for children aged 2 to 12

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

People who should get the vaccine but are not at risk of getting complications include those who:

  • work in healthcare
  • are a carer or live with someone who is at a risk of flu
  • are in regular contact with pigs, poultry or water fowl

Read more about flu vaccine for healthcare workers

Vaccines needed during pregnancy - flu vaccine

Where to get the flu vaccine

  • your GP surgery
  • a local pharmacy 
  • an occupational health department if you work in healthcare

How the flu vaccine works

The flu vaccine helps your immune system to produce antibodies to the flu virus. If you then come into contact with the virus, these antibodies will attack it and stop you from getting sick.

The flu vaccine starts to work within 2 weeks.

You need to have the flu vaccine every year. This is because the antibodies that protect you decline over time. Flu strains can also change from year to year.

The flu vaccine doesn't contain any live viruses. This means it can't give you the flu.

Safe and effective flu vaccine

Getting the flu vaccine is the best way to help protect yourself from getting the flu.

It will not stop all flu viruses and the level of protection may vary. So it's not a 100% effective and you may still get flu.

But if you do get flu after you have the vaccine, it's likely to be milder and you will recover more quickly.

Flu vaccines usually reduce the risk of infection by 40-60%.

Flu vaccines also reduce:

  • the severity of illness
  • complications from influenza
  • flu-related hospitalisations
  • admissions to critical care units

Flu vaccines have been given to millions of people worldwide for over 60 years, including to pregnant women. Reactions are generally mild.

There is no thiomersal (mercury), gelatin or porcine gelatin in the 2020/2021 flu vaccine.

Flu vaccine side effects

You may have a mild fever and aching muscles for a couple of days after having the vaccine. Your arm may also be a bit sore where you got the injection.

Serious side effects of the flu vaccine are rare.

When you should not get the flu vaccine

You should not get the flu vaccine if you:

  • have had a severe allergic (anaphylaxis) reaction to a previous flu vaccine or any part of the vaccine. 
  • are taking medicines called combination checkpoint inhibitors, for example, ipilimumab plus nivolumab
  • are ill with a temperature greater than 38 degrees Celsius , you should wait until you are well before getting the vaccine.

If you have an egg allergy, you can get a different dose of the vaccine. Talk to your GP.

Content supplied by the NHS and adapted for Ireland by the HSE

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This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.

Page last reviewed: 12 June 2019
Next review due: 12 June 2022