Vaccine development and safety — COVID-19

From the start of the pandemic, scientists around the world have worked to create vaccines to help prevent severe illness from COVID-19. These vaccines were created in a safe and regulated way, as quickly as possible, to save lives.

Developing and testing the COVID-19 vaccines

Scientists used existing vaccine technology and some medical technologies that were new to vaccines, like mRNA, to explore ways of creating COVID-19 vaccines that worked and were safe to use in the general population. You can read more about the scientific process of vaccine creation on the CSIRO website.

Once a vaccine has been developed, it needs to be manufactured and tested for safety. All vaccines go through trials and tests as they are developed and before they are approved for use. This includes being tested on thousands of volunteers before they are approved. Testing happens in three main phases.

Phase 1

Phase 1 clinical trials usually include a few dozen healthy adult volunteers and focus primarily on assessing safety and demonstrating that the vaccine works.

Phase 2

Phase 2 clinical trials have hundreds of volunteers and can include sub-groups such as older adults, children or people with pre-existing medical conditions. These trials aim to show the vaccine prompts an effective immune response in different people and confirm that it is safe.

Phase 3

Phase 3 clinical trials include many thousands of participants and aim to show that a vaccine is effective in preventing people from the general population getting the disease. Phase 3 trials also thoroughly assess the vaccine for safety and side effects. This phase often also involves placebo groups comparing the response of people who receive a non-COVID-19 vaccine against the real product.

For the COVID-19 vaccines, no testing phase has been skipped. Instead, some of these phases have been combined, or run at the same time as each other. Having these ‘overlapping’ timeframes has helped test COVID-19 vaccines quickly and help make them available to save lives earlier.

Ongoing safety monitoring

The TGA actively monitors the vaccine safety after a vaccine has been made available in Australia and investigates any potential new safety issues.

The National Centre for Immunisation Research and Surveillance also collects data on and monitors the safety of COVID-19 vaccines in Australia.

Choosing vaccines for Australia

In Australia, the Government requires robust scientific data and analysis before a new vaccine is allowed to be given to the population. The Australian Technical Advisory Group on Immunisation (ATAGI) and the COVID-19 Vaccine and Treatments for Australia – Science and Industry Technical Advisory Group advise the Australian Government on which vaccines are effective and safe.

Long-term effects of COVID-19 vaccines

Like all medicines, COVID-19 vaccines do not last long in your body. The ingredients in vaccines degrade within a few days, and it takes a few weeks for your body’s immune response to develop. When there are rare but serious side effects from vaccines, they occur within the first few weeks, while your immune system is being activated.

Rare side effects

There is a very rare and serious risk of Thrombosis with Thrombocytopenia Syndrome (TTS) with the AstraZeneca (Vaxzevria) COVID-19 vaccine and myocarditis or pericarditis from Pfizer (Comirnaty) and Moderna (Spikevax) COVID-19 vaccines. It is important to know that these side effects took a long time to discover because they are so rare, but that doesn’t mean they develop a long time after receiving the vaccine.


Immunity from vaccination is much less risky than immunity through exposure to a pathogen like the virus that causes COVID-19. We do not have long-term research on health outcomes of COVID-19, however we do know the virus can damage the lungs, heart and brain, even in mild cases, which increases the risk of long-term health problems.

More information about COVID-19 vaccine safety

Australians are encouraged to rely on reputable sources of information to help them make informed choices and stay up to date.

Information will be communicated through government channels, as well as states and territories and the health sector.

Reputable information about vaccines is available from: