Every single question you have about vaccine boosters, answered by an expert.

Earlier this week, Australian Technical Advisory Group on Immunisation (ATAGI) shifted its advice on COVID booster shots, reducing it from six months to five after the second vaccination.

Since then, we’ve also had to deal with rocketing case numbers, the increasing threat of Omicron and ever-changing restrictions. 

We’ve been confused. We've been anxious. We've been overwhelmed.

And now we have all the questions.

Watch: Epidemiologist Maria Van Kerkhove addresses the World Health Organisation. Post continues below. 

Video via @WHO/Twitter.

What are vaccine boosters? 

So, studies have shown that a reduction in our protection from COVID-19 occurs five months after our second primary vaccination. Therefore, an additional booster dose is recommended. 

In Australia, there are two booster doses that are readily available: Comirnaty (Pfizer) and Spikevax (Moderna). 

What you may be surprised to learn is that the booster is actually no different to the primary vaccinations; it’s all a matter of dosage. 

Leading infectious diseases expert Professor Sharon Lewin is director of Melbourne’s Doherty Institute in Melbourne, and co-chair of the National COVID-19 Health and Research Advisory Committee, which provides advice on Australia’s health response to the Commonwealth chief medical officer. (Yes, basically, she is very much in the know.)

As Professor Lewin told Mamamia, “The Pfizer third shot is exactly the same as dose one and two. The Moderna is a half dose.”

Professor Sharon Lewin. Image: Getty. 


Does everyone need a booster dose? How soon?

ATAGI recommends a booster dose for anyone who is 18 years and older, and has had their second COVID-19 vaccination dose at least five months ago. 

And according to Professor Lewin, there are “no problems with supply”.

For those with increased exposure risk (e.g occupational risk, those in outbreak areas or who have risk factors for severe disease), ATAGI stresses the booster dose is of particular importance. 

It also recommends the booster dose for anyone with immunocompromising conditions, a minimum of just two months after their second dose.

And even if you’ve been infected with COVID-19 already, you still should get the booster, says Professor Lewin.

“The recommendation is to wait about three months [since infection].”

So, just how important is it to get the booster?

Professor Lewin puts it simply: 

“It is really important - especially with Omicron. Super important,” she reiterated.

Essentially, boosters provide us greater and earlier protection against infection from the virus that causes COVID-19, severe disease, and yes, even death. 

“The third shot gives you much higher levels of antibodies than the first two doses,” tells Professor Lewin. 

While it’s not mandatory, ATAGI believes the booster is vital in order “to mitigate against waning immunity” and the emergence of variants.

And according the Department of Health, a booster will not only provide protection, but it “should help prevent spread of the virus” too. 

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Should we be getting the booster earlier than the five month mark?

Not at this stage. 

While the initial interval between primary and booster doses was six months, considerable data suggests that five months is the sweet spot. 

Professor Lewin gives us some insight as to how the judgment on the booster timeframe is made:

“The decision is based on a mix of what your antibody levels are doing, what your T cells are doing - [they are] another arm of the immune system we know less about, but are important in protecting us from getting very sick with COVID - and safety.”


Given the ever-evolving nature of COVID-19 variants, research too continues to progress (and remember, Omicron was only first reported in South Africa just three weeks ago.)

As it stands, most data relates to five months post-second vaccination, and little exists around the two month mark.

“The safety issues are really important - and you only know safety from clinical trials. So, you can't just assume that if you give the third dose at two months, it will have just the same risk side effect profile as if you give it at five months. It might be exactly the same, but we actually don't know.” 

And so, for now it’s about managing that risk benefit profile, and that could continue to change as more data becomes available from countries that have rolled out boosters earlier than Australia. 

Israel was the first country to administer boosters in July. What lessons can we learn?

Professor Lewin says the key lessons have been “that boosters work in both reducing infection and reducing hospitalisations; and the risk of hospitalisation, especially in elderly populations.”

That’s right. As published in medical journal, The Lancet in October, “…Adding a third dose was estimated to be 93 per cent effective in preventing COVID-19-related admission to hospital, 92 per cent in preventing severe disease, and 81 per cent in preventing COVID-19-related death, as of seven or more days after the third dose.”

But how effective is the booster in protecting us against Omicron? And will it become mandatory?

Just as well, we have some data now starting to file in on that too. 

On Saturday, director of the Infectious Diseases Unit at Israel’s Sheba Medical Centre, Gili Regev-Yochay, told Reuters“The good news is that with the booster dose it increases [protection] about a hundred fold. There is a significant protection of the booster dose, [but] it is lower than the neutralization ability against the Delta, about four times lower”. 


Numbers aside, Professor Lewin says another lesson Australia has observed from Israel, is that everyone who has had their first and second dose, “doesn’t automatically line up for their booster”.

As such, in October, Israel mandated the booster vaccine as a requirement for a valid digital vaccination passport.  

“I don't think we can be complacent about the third dose and we need to track carefully. So far, people are lining up and getting it, which is great. But we need to watch that closely,” comments Professor Lewin.

“We will review all this in January to make a decision on that very issue.”

Do we need the same brand of booster as we had for our first vaccinations? 

While Professor Lewin concedes there is a “theoretical benefit” to mixing, overall, she doesn’t believe it makes a difference.

Both Pfizer and Moderna are mRNA vaccinations, she points out, and “mRNA gives you the best boost, no matter what you had first” - even if that was AstraZeneca. 

Referring to a recent large UK study which tested nine different boosters on top of AZ/AZ or Pfizer/Pfizer, Professor Lewin continues, “All the vaccines that used mRNA, in either Pfizer or Moderna, gave the biggest boost of antibodies for both people that had AZ/AZ or had Pfizer/Pfizer.”

How safe are the booster doses? Are there any side effects? 

“There's no indication that there's additional adverse events when the dose is given at five to six months,” reassures Professor Lewin.  

“We still see reactogenicity, which is, fever, feeling aches and pains, flu-like symptoms for the first 24 to 48 hours, but that's okay; inconvenient, of course.”

And interestingly, early reports on the Pfizer booster show that the risk of heart inflammation - highest amongst young men - is reduced by “about half”, in comparison to the second dose, tells Professor Lewin. 


Hoping to visit family in the UK over Christmas, Laura was eager to get her booster earlier this month. 

“I didn't really have any side effects apart from a sore arm and maybe a bit of fatigue, so I was lucky!,” she told Mamamia.

“I feel very reassured - especially now in the face of the Omicron variant, and know I have done as much as I can to protect myself, my family and the wider community."

Image: Getty.

Will the booster be our final vaccination against COVID? Or will it become like the annual flu shot?

Basically, it’s still too soon to tell. 

ATAGI says, “There remains uncertainty about the duration of protection following a booster dose, and the potential emergence of future new variants”.

Professor Lewin adds, “Whether this is a three dose regimen to give you a really good, durable immunity, or whether there'll be annual boosters, we just don't know.”

How long until we do know?

Probably over the next few months as more data filters through, she anticipates.

How do I go about getting a booster?

You may have already received a letter encouraging vaccine boosters from the federal government, or perhaps a text message reminder from your state government. In any case, if you had your second vaccination five months ago (or two months ago and you're immunocompromised), and you're 18 years or over, get cracking, and book a booster dose. How? Call your GP or use the COVID-19 Clinic Finder.

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Feature Image: Getty.