‘Simply not seeing that yet’: it’s still too early to say vaccines are having an impact in Australia
As new daily Covid cases in Australia continue to hit highs, experts say it is too early to tell whether vaccines are having an impact on hospitalisations and deaths.
Both Scott Morrison and Gladys Berejiklian have recently claimed that the vaccination rollout so far has led to lower hospitalisations and deaths.
But experience from around the world and our own outbreaks last year shows that hospitalisations tend to lag case numbers by about 10-14 days. Deaths can lag cases by as much as 30 days. And while hospitalisations are lower than they were last year, they’re still trending in the wrong direction.
So far there have been far fewer cases among older Australians since the current outbreak began than preceding it. Older Australians were prioritised in the vaccine rollout, and this may show some success in shifting the risk away from the most vulnerable.
“Our numbers are just too small currently to see the impact of our (low-ish) vaccination rates,” Prof Paul Glasziou, the director of the Institute for Evidence-Based Healthcare at Bond University, said.
Prof Adrian Esterman from the University of South Australia said that if vaccines were having an impact then it was mixed, with positive signs in the numbers of hospitalisations and deaths, but not in new cases.
“If the vaccines were working, and this is what Scott Morrison and [Gladys Berejiklian] have been saying, then we would expect case numbers to go down for current outbreaks. And for there to be much fewer major outbreaks in the future,” Esterman said.
“But we are simply not seeing that yet and not in the near future.”
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Even with the significant increase in cases recently, the federal health department’s epidemiology reports show less than 100 cases among those aged over 80 since the beginning of June this year.
Glasziou said vaccines were “very likely” to have helped older age cohorts, but noted there had also been changes in aged care processes. This made it hard to draw a causal link to vaccines.
Outbreaks in aged care facilities were a significant driver of both cases and deaths last year, with the University of New South Wales epidemiologist Prof Marylouise McLaws describing residents as a “captive audience”.
There had not been similar outbreaks in aged care during the current outbreak even with the slow vaccination rollout for aged care workers.
But younger Australians were being infected at alarming rates. Last week a 15-year-old boy in south-west Sydney became the first person aged between 10 and 19 to die from Covid in Australia.
“The fly in the ointment is that eventually we shall start seeing hospitals filled up with younger people and there will be deaths in younger people” Esterman said.
“We are seeing all over the world, in places like the UK, that it is now young people getting infected. And young people going to hospital. And, occasionally, young people dying.
“So even though case numbers have gone up in those countries, hospitalisations and deaths are going down. And that’s because, basically, the virus, the Delta variant, is now mainly infecting those who are not fully vaccinated.”
The latest vaccination data showed very few younger people were vaccinated in Australia, as many had not been eligible until recently.
One promising sign throughout the current outbreak had been the steady drop in the percentage of positive cases that were in hospital – which was significantly below last year’s highs.
But even this may not be a reliable indicator of vaccine efficacy, as Prof Emma McBryde, an epidemiologist at James Cook University, noted that it was a bit too soon to draw inferences from the number of hospitalisations as to “some extent hospitalisations are influenced by capacity and decision making about admission for isolation”.
The latest epidemiology report released by the federal health department showed the case fatality rate (CFR) – the number of deaths divided by cases – was significantly lower in the year to 1 August – 0.28% – than it was in the same period last year – 2.75%.
There had been an increase to 0.45% between 19 July and 1 August, and there had been more deaths since the last epidemiology report was released.
However, it might be too soon for even this measure. The number of identified infections was not the same as actual infections – we may be missing some cases. This was especially problematic for comparisons to other countries. And Glasziou said our numbers were too low for CFR to be a reliable indicator.
“Yes, CFR will come down as vaccines go up, but [it’s] probably undetectable in Australia just now,” Glasziou said.
Notes and methods:
Covid cases by age compiled by going through fortnightly federal health department epidemiology reports. Cases for the period ending 18 July were adjusted due to a change in reporting period
Data on deaths and vaccinations by age group were scraped from federal government pdfs by Ken Tsang