About flu vaccines

What’s in a flu vaccine?

New Zealand’s 2021 flu vaccine protects against four strains of flu virus – two influenza type A strains and two influenza type B strains:

  • A/Victoria/2570/2019 (H1N1)pdm09-like virus
  • A/Hong Kong/2671/2019 (H3N2)-like virus
  • B/Washington/02/2019-like virus
  • B/Phuket/3073/2013-like virus

The first two are new strains for 2021.

Throughout the year, the World Health Organization 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.

The vaccine:

  • does not contain any live viruses and so cannot cause flu 
  • does not contain any preservatives, thiomersal or mercury 
  • contains only very tiny amounts of egg protein and is safe for people with egg allergies.

How does it work?

The vaccine contains harmless parts of four flu viruses, not the whole virus. When you are given the flu vaccine, your immune system reacts to the parts, makes cells and a special type of proteins called antibodies that will protect you against the four types of flu virus, if you come into contact with them later.

Your flu vaccine can only protect you against flu, it cannot protect you against COVID-19, the common cold or other viruses and diseases in circulation.  Flu vaccines cannot give you flu.

How well does it work?

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 immunisation for the body to start protecting against flu. 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.