What impact are boosters having on illness and death in Australia?

In many respects, Western Australia has stood apart from the rest of the nation during the pandemic in a sense far wider than its geographical isolation.
 
The state’s government has shut its borders for longer, maintained more restrictions, and enacted a more extensive vaccine mandate – covering up to 75% of the workforce – than anywhere in the country.
 
So where has that left around 2.7 million West Australian residents now that the virus is circulating widely?
 
The restrictions may finally be easing, but for now the state still seems to stand apart – and the difference is attracting some attention.
 
South Australia and Queensland are the states with the most readily comparable trajectories, having adopted a similar suppression strategy for much of the same time as Western Australia.
 
However, the number of people dying from the illness has climbed notably more sharply in both those states.
 
As of 1 April, it is 35 days since Western Australia first recorded 1000 daily cases (on 25 February). There have been 40 COVID-19 deaths registered since that point, with ICU rates broadly staying below double figures.
 
By comparison, South Australia was recording 1000 daily cases by 29 December. In the same 35-day timeframe afterwards, 116 COVID-19 patients had died – although the ICU rates have remained roughly parallel.
 
Given South Australia’s smaller population, the difference is all the more striking.
 
In Queensland, the case numbers began to rise exponentially at the same time as South Australia, hitting 1000 daily cases on 28 December. In the 35 days since that date, a further 227 deaths caused by COVID-19 were recorded.
 
Queensland has around twice as many people as Western Australia, but the death rate was five and a half times higher.
 
The long tail of the Delta wave in states like New South Wales and Victoria makes those populations harder to compare, but the underlying pattern appears similar.
 
It is a trend that has been noted at the heart of the pandemic response.
 
Higher booster coverage
Dr Lucas de Toca, who leads the Federal Government’s primary care response to the pandemic, remarked on it in a recent COVID-19 response update webinar, and attributed the difference to the higher booster rate in Western Australia.
 
The latest rollout figures do indeed show a gulf in booster rates. In Western Australia, 86.2% of eligible adults have had a third dose, with the ACT next – more than 10 percentage points behind at 75.3%.
 
‘We can see what the Omicron wave in the eastern states as the booster [program] was commencing looks like, versus the wave in WA where booster rates were already high at the time of Omicron commencing,’ Dr de Toca remarked.
 
‘Their impact on case numbers as a whole but also hospitalisations, severe disease and deaths is very marked.’
 
Professor Catherine Bennett, Deakin University Chair of Epidemiology, warns that precise comparisons are hard to make.
 
She notes that states record figures in varying ways and will have different degrees of success in capturing the true number of COVID-19 cases, with the official figures believed to be half or less of the true infection tally.
 
However, while she believes it is too early to tell if the pattern in Western Australia will endure, she believes the difference is striking.
 
‘What has been reassuring to me all the way through is that the ICU rates are very low,’ Professor Bennett told newsGP.
 
‘Even though case numbers have pushed up, [Western Australia] is still peaking at double figures every few days in ICU.
 
‘And that’s quite extraordinary.’

Professor Bennett notes too that has happened despite case numbers climbing more steeply in Western Australia than she believed they would due to new, more transmissible types of SARS-CoV-2.
 
‘No one knew BA.2 was coming, but it turns out boosters are more effective than we even hoped they might be against this,’ she said.
 
‘Combining [vaccination] with past infections that might work for other states going ahead, but with such a low infection history in WA, the boosters were even more important.’

Professor Catherine Bennett believes it is too early to tell if the pattern in Western Australia will endure.
 
Luck, she believes, has played a part, with potentially dangerous outbreaks not spreading in Western Australia as they might have.
 
Professor Bennett also notes the difficulty in trying to assess the influence of restrictions in movement, border closures, masks and other measures.
 
‘You will not know whether all the other things did nothing, or did everything or something in between,’ she said.
 
But while Professor Bennett believes other measures are playing a part, she identifies the booster rate as the obvious distinguishing characteristic.
 
‘With Omicron, the chances are [the other interventions] are doing less as time goes on, and you’re actually leaning more on your booster rate than on the other interventions,’ she said.
 
WA Health has also released figures that underline the health impacts on those who are not protected by vaccination. As with the early figures in the Delta wave in New South Wales, the unvaccinated are disproportionately over-represented in hospital, with almost a third of those in Western Australian hospitals due to COVID-19 having no vaccine protection, despite making up less than 5% of the population.
 
The impact of mandates
Professor Peter Richmond is an immunologist at Perth Children’s Hospital and also leading a vaccine trials group for the Wesfarmers Centre of Vaccines and Infectious Diseases. The work is looking at the effect of combining different vaccines booster types, as well as what gap might be needed between boosters, and their impact on different variants.
 
He has ‘mixed feelings’ about the widespread mandate in Western Australia but says that whatever the political dimensions, the impact on a state that once had one of the country’s slowest vaccine uptake rates is clear.
 
‘For where WA was at that stage, it is a tool that appears to have been quite effective,’ he told newsGP.
 
‘Not everyone would agree with it, but they can’t deny [WA has] achieved very high coverage.’
 
Professor Richmond also attributes the comparatively low death and hospitalisation rates in Western Australia directly to the elevated booster uptake.
 
‘I do think it shows the benefit of having the extra booster coverage,’ he said. ‘It has impacted on the burden on our healthcare system and it should be celebrated.’
 
Professor Richmond thinks other states should still be trying to catch up, but acknowledges they would find it hard to put mandates in place at this stage.
 
And while his research is still underway, the question for him is not if the boosters are beneficial, but to what extent.
 
‘To be honest, it’s never too late because even if you’re an older person who’s been infected after two doses, getting a third dose will give you better, not only long-term protection, but also breadth of protection,’ he said.
 
‘That’s fairly clear.’
 
Log in below to join the conversation.

boosters COVID-19 Omicron vaccination