Like any medication in development, vaccine candidates must undergo rigorous testing procedures and scientific evaluation to prove not only their effect on the targeted disease, but also to determine their safety, before being licensed and registered for use in vaccination programs. In Australia, the Therapeutic Goods Administration (TGA) is responsible for assessing vaccines and other medicines for use in Australia.

Once vaccines have been introduced into the community, the safety and effectiveness of vaccines then continues to be monitored in the post-licensure phase through active surveillance programs and further post-licensure trials. This is to ensure that there is ongoing monitoring for how the vaccines are working in the ‘real-world’, noting they will be administered to a much larger and more diverse population than during the development phase.

Development phase

During vaccine development, initial safety testing of a vaccine candidate occurs in two stages. Stage one involves pre-clinical assessment in the laboratory. Stage two involves the evaluation of the vaccine candidate in three phases of human clinical trials. If a vaccine candidate is not deemed safe in any stage, it cannot progress into the further stages of clinical trials, with this data being reviewed by an independent data safety monitoring board (DSMB).

  • Phase I clinical trials: the vaccine candidate is given to small numbers (25–50) of healthy adults with the primary goal of assessing safety.
  • Phase II clinical trials: if the vaccine candidate is found to be safe in Phase I, it is then given to hundreds of people to determine how effectively it stimulates immune responses, the optimal dose regimen, and whether there are any side effects.
  • Phase III clinical trials: if the vaccine candidate is found to be effective and safe in Phase I and II, it is then given to many thousands of people to test whether it protects large populations from the target disease and to determine if there are any uncommon or serious side effects.

A vaccine must pass all of these phases before it is registered for use by the TGA. Previously, approval of vaccines could take up to 10 years. However, the process has been streamlined throughout the COVID-19 pandemic and can now be completed in under 12 months, noting all of the appropriate clinical phase trials and data requirements from the regulators have not changed.

Post-licensure phase

Despite the extensive safety testing undertaken in clinical trials before a vaccine is licensed, some side effects are so rare, they cannot be detected in a trial population (e.g., such as with thrombosis with thrombocytopenia syndrome [TTS] following COVID-19 adenoviral vector vaccines). In addition, the efficacy of a vaccine may be different when given to a larger and more diverse population compared with those who participated in the clinical trial (e.g., due to the presence of underlying medical conditions, different age groups etc). For these reasons, assessment of safety and efficacy continues to be monitored in post-licensure assessments through:

  • further clinical trials
  • surveillance of the impact of the vaccine on the disease it aims to prevent using networks such as PAEDS
  • surveillance of adverse events following immunisation using systems such as AusVaxSafety and reporting services like SAFEVAC और सैफविक.

What happens if a problem is suspected?

Any suspected vaccine safety signals undergo a thorough investigation by the TGA, with the support of the jurisdictional vaccine safety services.

If a suspected problem could be serious, authorities will consider a range of actions including modifying the product information (PI) and if extremely serious it may include suspending use of the vaccine during the investigation.

Provisional approval

Provisional approval has been the formal pathway used in Australia for speeding up access to COVID-19 vaccine candidates using preliminary clinical data. The provisional pathway allows for the temporary registration of promising medicines or vaccines based on early data, where the benefits of early access (such as in a pandemic), outweigh any risks.

It is very important to note that this evaluation process remains a full review and a vaccine is still required to pass all the same phases of clinical trials and meet the same requirements for safety and efficacy as any other vaccine in development.

As further clinical data to confirm the safety of a vaccine becomes available, full registration can then be granted (On April 21, 2023 Spikevax (Moderna) was transitioned from the provisional pathway to full registration).

Health Technology Assessment (HTA) of vaccines

Whilst vaccines are undergoing development and regulatory approval, in parallel they also need to undergo health economics assessment if they are going to go onto the National Immunisation Program (NIP). In Australia this assessment of vaccines is undertaken by the Pharmaceutical Benefits Advisory Committee (PBAC).

This pathway was not utilised during the COVID-19 pandemic, due to the speed and complexity of the public health emergency, but PBAC approval will be required for all new vaccines that are coming down the pipeline. As part of this assessment, ATAGI provides advice to the PBAC regarding how these vaccines may be best utilised in the Australian context, taking into account vaccine effectiveness, safety and equity.


लेखक: Georgina Lewis (Clinical Manager SAEFVIC, Murdoch Children’s Research Institute) and Rachael McGuire (SAEFVIC Research Nurse, Murdoch Children’s Research Institute)

द्वारा समीक्षित: Georgina Lewis (Clinical Manager SAEFVIC, Murdoch Children’s Research Institute), Rachael McGuire (SAEFVIC Research Nurse, Murdoch Children’s Research Institute) and Nigel Crawford (Director SAEFVIC, Murdoch Children’s Research Institute)

तारीख: 10 मई 2023

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