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 trials. This is to ensure that there are no issues that may have been missed during the development phase.
During vaccine development, initial safety testing of a vaccine candidate occurs in two stages. Stage one involves preclinical assessment in the laboratory. Stage two involves the evaluation of the vaccine candidate in three phases of clinical trials. If a vaccine candidate fails the safety tests performed in stage one, it cannot progress further into the stage two clinical trials.
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; to determine 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. Approval of vaccines can take up to 10 years.
Despite the extensive safety testing undertaken before a vaccine is licensed, some side effects are so uncommon, they cannot be detected even after studying a vaccine in thousands of people. For this reason, post-licensure assessment is performed.
Safety and effectiveness continue to be monitored using a variety of mechanisms. These may include:
- 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 AEFI-CAN and SAEFVIC
What happens if a problem is suspected?
Any suspected problem with a vaccine signals the need for a thorough investigation by the TGA.
If a suspected problem could be serious, authorities will consider a range of actions including suspending use of the vaccine during the investigation.
- Australian Government Department of Health: Are vaccines safe?
- Australian Academy of Science: How are vaccines shown to be safe?
- Australian Immunisation Handbook: Fundamentals of immunisation
- The International Coalition of Medicines Regulatory Authorities: ICMRA statement about confidence in vaccine safety and effectiveness (for healthcare professionals)
- The International Coalition of Medicines Regulatory Authorities: ICMRA statement about confidence in vaccine safety and effectiveness (for the general public)
Authors: Georgina Lewis (Clinical Manager SAEFVIC, Murdoch Children’s Research Institute)
Date: July 2020
Materials in this section are updated as new information and vaccines become available. The Melbourne Vaccine Education Centre (MVEC) staff regularly reviews materials for accuracy.
You should not consider the information in this site to be specific, professional medical advice for your personal health or for your family’s personal health. For medical concerns, including decisions about vaccinations, medications and other treatments, you should always consult a healthcare professional.