A woman receives a COVID-19 vaccination at the Australian Sikh Association pop-up clinic in Sydney in August.
A woman receives a COVID-19 vaccination at the Australian Sikh Association pop-up clinic in Sydney in August.
9 min read



Australia is rolling out COVID-19 booster shots. Here's how they work

From 11 October, some people in Australia will be able to access a third vaccination, known as a booster shot, to improve their protection against COVID-19. Here's what we know so far.

Published Saturday 9 October 2021
By Biwa Kwan
Source: SBS News

Australia's expert panel on vaccines has approved the rollout of a third dose of a COVID-19 vaccine for those with severely weakened immune systems, with advice to be released later this month for the general population.

"The third dose is intended to maximise the level of immune response to as close as possible to the general population," the Australian Technical Advisory Group on Immunisation (ATAGI) said in a statement. 

Who will get the booster shots first? 

Federal Health Minister Greg Hunt said the government is prioritising the 500,000 Australians with the most weakened immune systems, including people with malignant cancers, organ transplants, and those born with immunodeficiencies.

From Monday 11 October, 500,000 Australians aged 12 and older who are considered "severely immunocompromised" according to a list specified by ATAGI, will be eligible to book a booster shot. 

The list includes people living with HIV that is not controlled by therapy, those receiving certain arthritis medications and people with an immunodeficiency.

People at the Boondall mass vaccination hub in Brisbane.
Source: AAP

Health experts are welcoming the move as a step forward for health equity. Dr Kylie Quinn, from RMIT University's school of health and biomedical sciences, said the move helps increase the protection for the most vulnerable. 

"This is a great outcome in terms of equitable outcomes for healthcare. We are really trying to catch people up. In people with severe immunodeficiencies, that third dose is really trying to get them into the same ballpark [of protection] as someone from the general population who has gotten two doses.

"But we also have to address anyone who is missing out on the first two doses."

How do booster shots work? 

The vaccine technology underlying the booster shots is the same as the first and second vaccine doses. 

Dr Emily Edwards from the Department of Immunology and Pathology at Monash University said the building blocks for booster shots draw from the knowledge developed from vaccines in the past, including for hepatitis and human papillomavirus (HPV) which form part of the immunisation programs in schools. 

"It is all about building blocks," she told SBS News. "The technology may have been there for years, and that is the case with the vaccines and with the immunological tools we use to monitor how you respond to the vaccine and the virus."

The booster shot is aimed at ensuring the level of immunity and protection from the earlier doses of the vaccine is maintained at a certain level as the effect from the antibodies wears off over time.  

Which booster shot should you get?

The ATAGI advice said the first preference would be to recommend the third dose be an mRNA vaccine, such as Pfizer or Moderna.

AstraZeneca can be used for the third dose for those who had it for their earlier shots and did not suffer any adverse reaction, such as anaphylaxis. 

Chief Medical Officer Paul Kelly said there is "flexibility" to use AstraZeneca if the side effects from the second dose of an mRNA vaccine contraindicate the use of that vaccine as the third shot. 

"A third dose is likely, at this stage, to be the last dose we have to do." 

"We know a lot about vaccines from other viruses. With hepatitis, for example, two or three doses is likely to give lifelong immunity. And that is what we hope for these."

How soon should you get a booster shot?

The recommended interval for the third dose for the severely immunocompromised is between two and six months after the second dose of vaccine.

In exceptional circumstances, such as an outbreak or intensification of immunosuppression, the interval may be reduced to four weeks. 

Bookings will be available for eligible people via a medical practitioner and Professor Kelly encouraged people to begin that discussion "as soon as possible and book in for a third dose". He said he would be writing to medical practitioners to provide them with guidance. 

Healthworkers at a drive-through COVID-19 vaccine hub in Melbourne.
Source: AAP

Professor Kelly indicated that for the general population, an interval of up to eight months after the second shot would be considered the likely time period before eligibility for the third shot.  

Dr Edwards said observation will be needed to determine what level of top-up is needed for the generation population and research was ongoing. 

"That information is coming through, which shows us what we need to generate an effective response [to COVID-19]. ... That will dictate then whether we need a booster because some people with certain vaccines might not require a booster. It will also dictate the timing of when that booster has to occur."

How effective are booster shots?   

The increased virulence of the Delta variant of COVID-19 has diminished frontline protection against catching the virus, but still maintains high levels of protection against severe hospitalisation and death

Dr Edwards said as Australian jurisdictions reopen and exit lockdown, other public health tools such as masks and physical distancing will still be necessary. But the effectiveness of vaccines still remains high - including for booster shots. 

"If you have a vaccine, you're more likely to be protected from that than someone who isn't. There will still be some infections, unfortunately. But it does mean it will still protect you against severe disease, which is really important, especially in this global pandemic."

Dr Quinn said studies from Israel, which moved to booster shots earlier than most nations after a rapid vaccine rollout, show that breakthrough infections were actually showing up in immunocompromised patients who were not responding to earlier vaccine doses, making the case for booster shots for this group. 

"They only make up 2 per cent of the population, this group of individuals. But, for example, in Israel, they were making up 40 per cent of the vaccinated people in hospital with COVID-19. So it is clear that we need to do more to help protect against that severe disease."

Dr Quinn said the data from Israel on the efficacy of booster shots needs more scrutiny, but anecdotal reports of booster shots on the general population show an immediate impact on hospitalisation rates. 

"And that would make sense because these third shots give an immediate boost to the immune response. It would probably provide that immediate protection. We still need to understand how durable that protection is."

She added that studies out of the UK and US demonstrate robust vaccine effectiveness in the booster shot. 

Dr Edwards said health companies are already trying to stay ahead of COVID-19 mutations, and how that could impact vaccine effectiveness. 

As for lifelong immunity, that is the holy grail, she said. 

"Immunologists and virologists, as time goes on, will learn more and more about ... how your immunity is maintained over time and whether it is required to keep having boosters for the rest of your life with this virus."

Are there any risks or side effects?

As the booster shots are the same vaccines used for the earlier shots, the advice on side effects is expected to track along the same lines. 

But health authorities around the world are closely observing any long-term effects. 

"The fact that other countries including the UK are six months ahead of us in terms of their vaccine regimen means we will get that information quicker and be able to respond to it in terms of timing and requirement for booster shots," Dr Edwards said. 

Dr Quinn said there have been small trials looking at immunocompromised people with third doses. A recent study tracked organ transplant recipients who received a third vaccine dose. 

"With this particular group of patients, there have been good studies that have shown that is clearly beneficial to receive that third dose."

When will booster shots be available for everyone?

Formal advice from ATAGI is expected by the end of October on how booster shots might be rolled out to the general population, including health workers and older Australians. 

Mr Hunt said there are enough supplies being negotiated to ensure everyone in Australia who wants a booster shot can have one. 

"We have over 150 million vaccines that are secured for the future, so we're able to implement that on the timeframe and with the urgency and immediacy that is suggested by ATAGI, if and when they provide that," he said, adding that the supply includes Pfizer, Moderna and Novavax. 

He said there is enough supply to accommodate a second booster shot, or fourth vaccine dose, if it is recommended by ATAGI. Although at this stage, it is believed that a third dose would be the last shot required. 

Do we have enough doses for everyone? 

Greens Senator Jordon Steele-John, who has cerebral palsy, said it is important that any gaps in the delivery of the first and second vaccine doses for vulnerable groups are remedied.

"It does worry me that we've just added 500,000 people to the list of folks that do need it [a booster shot] in a context where we haven't fully vaccinated the suite of people that urgently need the first and second dose," he said.

Nationally, 60 per cent of adults aged 16 years and over are fully vaccinated. First dose coverage is at 80 per cent. 

Infectious diseases expert Sanjaya Senanayake said internationally, the discussion of booster shots in rich nations has put the spotlight on vaccine equity as it applies to the provision of first and second doses for developed nations.

"At the end of the day, if we're protected from severe illness and hospitalisation [in Australia], we should try and help the rest of the world," he said. "We have to be selfless to be selfish when it comes to COVID-19 and vaccination," he added, referring to herd or population-wide immunity in the Asia-Pacific region. 

WHO tells rich countries to stop ordering booster shots

Professor Kelly said ensuring vaccine coverage in developing nations in the region is important to thwart the emergence of variants of concern. 

"It is very important that we do support the whole world in this pandemic because that is where variants of concern will come."

Mr Hunt said 60 million doses have been allocated for developing nations and more will be provided "if there are additional doses available within Australia". 

Professor Kelly said regardless of booster shot eligibility, the status of being 'fully vaccinated' translates to two vaccine doses at this stage.

Additional reporting: Shuba Krishnan

Read more from the Vaccine in Focus series.