Boosters are coming: What does the latest evidence suggest?

Federal Health Minister Greg Hunt has confirmed Australia will ‘likely’ begin offering COVID-19 vaccine booster shots in the coming weeks.
 
‘Would I like to see [a booster program] commenced this year and do I expect it to commence this year? Yes and yes,’ Minister Hunt said on Wednesday.
 
‘We want to commence that in the second week of November, subject to advice that we have and confirmation both from ATAGI [The Australian Technical Advisory Group on Immunisation] and from the TGA [Therapeutic Goods Administration].
 
‘We’re ready, we’re in a position to commence, and to make sure that additional protection is provided.’
 
The announcement follows recent calls from some healthcare workers in Australia that further immune protection be delivered as quickly as feasible, given the much greater spread of the virus in the past four months, and the gradual opening up of the country.
 
Severely immunocompromised people have already begun receiving a third vaccine dose as part of a primary course following last week’s recommendation from ATAGI, which has also flagged a potential need for a booster program.
 
Minister Hunt told reporters aged-care workers and residents would be the first to be receive a third booster shot – an extra dose of Pfizer – followed by the rest of the general population.
 
Pfizer is currently the only vaccine manufacturer that has submitted data for approval for a booster vaccination, making it likely to be the only vaccine used in the initial stages of the rollout.
 
What is the latest evidence on boosters?
Since an article appeared in The Lancet last month suggesting there is not yet enough evidence for broad booster program, a pre-print study looking at Israel, the country that pioneered their use in July, has been published showing some impressive early signs of extra protection.
 
The study draws on Israeli medical data for 4,621,836 individuals, comparing rates of infection, severe disease and death between those who have had a booster and those who had received only the initial two doses of Pfizer.
 
It cites infection rates that were up to 10-fold lower in the booster group compared to the non-booster groups, with severe illness rates also showing a dramatic fall in the 40–60 and over-60 age groups.
 
Professor Dale Godfrey, Immunology Theme Leader at the Doherty Institute, believes the Israeli study is an important piece in a rapidly emerging body of evidence.
 
‘It is one of several studies that are all pointing to the same thing,’ he told newsGP. ‘As good as these vaccines are, like any vaccine they are not perfect.
 
‘But the booster makes a very big difference. And the difference appears to be prolonged – at least for the duration of the study, which is only two months.’
 
Professor Peter Collignon, an infectious diseases physician who also works at the Australian National University Medical School, told newsGP the Israeli study is ‘one of the most convincing yet’ on boosters, but believes there are possible confounders that might distort the results.
 
The pre-print study also acknowledges limitations, stating that biases might include differences between the behaviour and comorbidities of booster recipients and those who did not receive it.
 
The results could also be a reflection on Pfizer, the vaccine used in Israel both for the initial rollout and the booster program, Professor Collignon believes.
 
‘It may be that for Pfizer, you needed three doses instead of two doses anyway,’ he said.
 
Professor Godfrey, meanwhile, says other studies present evidence of enhanced protection that is less open to interpretation.
 
‘As always, with human analysis there’s always the potential for predisposing factors that could [have an] impact,’ he said.
 
‘In other studies, if you look at the neutralising antibodies that are induced with a booster vaccine, they go up quite a lot. That is one important factor that can provide protection against everything from infection through to severe disease.
 
‘So far, all of the studies I’ve seen, whether it’s for Pfizer, Moderna, or some of the other vaccines too, are suggesting that a third injection is increasing protection substantially, including protection against severe disease and death.’
 
However, he believes there is less evidence so far on whether the third dose carries a similar risk of adverse events, citing the elevated – but still rare – risk of myocarditis, particularly after a second dose of mRNA vaccines.
 
‘We don’t know yet whether a third booster dose is the same risk as it is after the second dose,’ he said. ‘You have to consider whether the extra level of protection from a third dose is worth the potential extra risk of other further adverse events.
 
‘The data is not clear on that yet.’


ATAGI has already recommended severely immunocompromised people receive third doses and flagged that a future booster program is ‘likely’.

Professor Collignon also believes the need for a booster shot will vary substantially – even within specific age groups – and says further carefully staged studies, including using placebos, are required.
 
‘It’s probably going to be an uneven distribution of people [who need a booster] – some have got much more underlying disease than others,’ he said.
 
He also believes that there is no need to fast-track booster shots for most people, including healthcare workers such as himself.
 
‘Most people aren’t even six months after vaccination yet. [Also], I reckon the best time we’re going to have in Australia is December till about May next year,’ he said.
 
‘We’re in a much better position [than northern hemisphere countries], with higher vaccination rates, better weather, better accommodation, and more recent vaccines.
 
‘So I do not think we have to rush this.’
 
Professor Collignon anticipates the greatest challenge to people’s immune systems will arrive next winter.
 
‘I think we should see what happens in Canada, the UK and Scandinavia, and other places and make our decision,’ he said.
 
‘And if we have to give lots of boosters, we can give [them] in February, March, April next year.’
 
Professor Godfrey also believes the seasons could be an important factor in the rollout of a booster program.
 
‘I think you can see the trends in the northern and southern hemispheres, the disease tends to spread more aggressively in the colder months,’ he said.
 
‘That’s not that surprising just by the way people behave and potentially by the way the virus can survive.’
 
High vaccination rates in Australia will remain an important factor in how we manage next winter, he believes – but the scenario will not be clear until closer to that time.
 
‘I think a big part of what will help us as we unlock and go back to relatively normal life is the fact that we’re coming into warmer months in Australia,’ Professor Godfrey said.
 
‘What happens beyond that, as we come back into the colder months, who knows?
 
‘It might be a time when we are wiser about vaccination waning and the impact of boosters, and that might change people’s thinking about how important it is to have a booster.
 
‘The information is emerging daily. I always feel concerned when I hear people talking with absolute confidence about what should or should not happen, because the data just isn’t in yet.
 
‘I’m always trying to keep an open mind about what’s going to be the best way forward.’
 
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