How effective is the flu jab and how it works

Although having the flu jab doesn’t guarantee you won’t catch the flu, it will give you more protection and reduce the symptoms if you do catch it.

Last updated: 31 March 2022

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How it works 

The 2022 flu vaccine contains harmless parts of four strains of flu viruses, not the whole virus. When you are given the flu jab, your immune system reacts to the parts, makes cells, and a special type of proteins called antibodies that will protect you against the flu. 

Your flu jab can only protect you against these four stains of flu, it cannot protect you against COVID-19, the common cold, or other viruses and diseases in circulation.   

The flu vaccine: 

  • is a subunit vaccine – it does not contain any live viruses  
  • does not contain any preservatives, thiomersal, or mercury  
  • contains only very tiny amounts of egg protein and is safe for people with egg allergies 
  • cannot give you flu. 

How effective is the flu vaccine? 

Sometimes getting a vaccine will not stop you getting flu, but it should stop you getting really sick.   

It takes up to 2 weeks after getting your jab for your body to start protecting against flu.  

For the best protection, you’ll need to get the flu vaccine every year because: 

  • protection against flu reduces over time 
  • each year flu can be caused by different strains of flu viruses that aren’t covered by the previous year’s vaccine. 

When the flu strains in the vaccine are a good match to the flu strains circulating in the community:  

  • around half to two-thirds of healthy vaccinated adults aged under 65 years of age will be protected against flu infection  
  • almost two-thirds of vaccinated adults who get flu will be protected from needing hospital care  
  • up to two-thirds of children who receive the vaccine will be protected from getting sick with flu 
  • about half to two-thirds of the immunised children aged 6 months – 17 years will be protected from needing hospital care for flu. 

2022 flu strains

Throughout the year, the World Health Organization (WHO) monitors the different flu strains around the world and each year decides which strains are likely to cause flu in the Southern and Northern Hemispheres.  

Flu vaccine manufacturers make each year’s vaccine by growing lots of these viruses, mostly in hens’ eggs. They then inactivate the virus and extract the bits that are needed to make the vaccine. 

New Zealand’s 2022 flu vaccine will protect against four strains of flu virus – two flu type A strains and two flu type B strains: 

  • A/Victoria/2570/2019 (H1N1)pdm09-like virus 
  • A/Darwin/9/2021 (H3N2)-like virus 
  • B/Austria/1359417/2021 (B/Victoria lineage) -like virus 
  • B/Phuket/3073/2013 (B/Yamagata lineage) -like virus 
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