How is vaccine safety demonstrated?

Flu vaccines are thoroughly tested before being made available to the public. Research and subsequent testing are essential steps in the development of a vaccine. The vaccine is first tested on animal models to demonstrate safety before it proceeds to human trials, which take place in three comprehensive phases.

Phase 1 Trials

A small group of healthy adults (around 25 to 50) are given vaccine shots, primarily to check that the vaccine is safe.

Phase 2 Trials

If the vaccine is deemed safe following a Phase 1 trial, it proceeds to the next stage, in which it is administered to a larger group of people.

This is done to assess a few important things:

  1. To determine if it activates the proper immune response; 
  2. To determine what dose and how many doses are needed to prevent a particular disease; and
  3. To identify any side effects.

Phase 3 Trials

When a Phase 2 trial shows that a flu vaccine is safe and effective, it progresses to a Phase 3 trial, in which it is administered to thousands of people. In this way, the vaccine is tested to see if it can protect large populations and to check for severe or unique side effects.

All vaccines administered to children must pass these three phases before being approved for use by the Therapeutic Goods Administration (TGA).

Are there unknown side effects?

There are a few cases where rare side effects have occurred following vaccination that have not been seen again. For this reason, continuous monitoring is carried out in communities to ensure total safety.

Any reports of adverse effects made by doctors and parents are subject to scrutiny, and those in authority will determine whether the review warrants further investigation. Links between vaccines and severe or rare conditions are also considered.

What happens during the investigation?

If any flu vaccine problem is identified, the TGA will intervene, and immunisation program managers and health authorities will also be involved in the investigation.

Some of the aspects that will be investigated include the manufacturing processes, vaccine quality and studies of unvaccinated and vaccinated individuals who have and haven't experienced reactions. If the problem is serious, the authorities may consider a range of actions, including suspension of the use of the vaccine.