The claim
Following a wave of coronavirus cases driven by the Omicron variant in December and January, Treasurer Josh Frydenberg defended the government's decision to move towards "normalised settings" for financial support related to the pandemic.
" … [W]e are always watching to see how the pandemic evolves. But what we do know as well is that the Omicron variant is 75 per cent less severe than the Delta variant and previous variants," Mr Frydenberg told Patricia Karvelas on ABC Radio's RN Breakfast program.
Is the Omicron variant 75 per cent less severe than Delta and other variants? RMIT ABC Fact Check investigates.
The verdict
Mr Frydenberg's claim is oversimplified.
It is clear from a variety of academic studies that Omicron causes less severe disease than Delta.
What is less clear is the magnitude of this reduced severity and the contribution of previous infection or vaccination.
Mr Frydenberg's claim is commensurate with two studies which were conducted in South Africa, but these studies do not unpick the relative reductions in the incidence of severe outcomes due to vaccination, previous infection and reduced virulence. A separate study from the same country estimated the latter to be 25 per cent.
And experts cautioned that the South African setting may not be comparable to the Australian setting due to differing age, vaccination, and previous infection profiles.
Studies in other countries have found a large range of lower reductions in risk to various clinical endpoints.
Another problem is that Mr Frydenberg's claim implies all variants other than Omicron are similarly severe to Delta.
But research has shown that other variants have different levels of severity. As one expert noted, it's not possible to compare them all with a single figure.
Experts said a comparison between Omicron and other, non-Delta variants made little sense, when those variants were no longer circulating widely.
Various variants
The existence of the novel coronavirus was first reported in December, 2019. The very first strain is often referred to as the "ancestral", or Wuhan strain.
Since it first emerged, the virus has been mutating, producing a number of variants with different epidemiological characteristics. The World Health Organisation names a variant with a letter of the Greek alphabet when it has been designated a "variant of interest" or a "variant of concern".
The WHO has working definitions of a variants of interest and variants of concern of SARS-CoV-2.
Variants of interest are classified as such when genetic changes are predicted or known which affect transmissibility, severity, immune escape, or diagnostic or therapeutic escape, and are causing significant community transmission in multiple countries.
Variants of interest
WHO label |
Pango lineage |
Earliest documented samples |
Date of designation |
|---|---|---|---|
Lambda |
C.37 |
Peru, Dec-2020 |
14-Jun-2021 |
Mu |
B.1.621 |
Colombia, Jan-2021 |
30-Aug-2021 |
Variants of concern are a confirmed threat to public health and are classified as such when an increase in virulence or transmissibility or a decrease in the effect of public health measures or diagnostics is observed.
Variants of concern
WHO label |
Pango lineage |
Earliest documented samples |
Date of designation |
|---|---|---|---|
Alpha |
B.1.1.7 |
United Kingdom, Sep-2020 |
18-Dec-2020 |
Beta |
B.1.351 |
South Africa, May-2020 |
18-Dec-2020 |
Gamma |
P.1 |
Brazil, Nov-2020 |
11-Jan-2021 |
Delta |
B.1.617.2 |
India, Oct-2020 |
11-May-2021 |
Omicron |
B.1.1.529 |
Multiple countries, Nov-2021 |
26-Nov-2021 |
It's not the first time Mr Frydenberg has made this claim.
In an earlier interview with Channel 7's David Koch, he said:
"The Omicron variant, Kochie, as we know, is 75 per cent less severe than previous strains."
And the same morning, he made the claim in an interview with Channel 9's Alison Langdon and Karl Stefanovic: "We do know that it's 75 per cent less severe than in previous variants."
There has been some discussion in the scientific community about the differences between the terms "variant" and "strain", but these terms are generally used interchangeably in colloquial discussion.
Measuring 'severity'
There is a spectrum of clinical outcomes produced by infection with SARS-CoV-2.
WHO provides "living guidance" for the clinical management of COVID-19, with definitions of mild, moderate, severe and critical disease.
The organisation defines these clinical presentations differently in adults and children, using oxygen levels, respiratory rates and " clinical signs of pneumonia (fever, cough, dyspnoea)".
The guidelines state that those with moderate disease may or may not require hospitalisation, but the management guidelines for severe disease, which include "proning" and supplemental oxygen therapy imply admission to hospital.
Mr Frydenberg spoke of relative severity, which can be measured by comparing one or more clinical outcomes, the most serious of which include hospitalisation, ICU admission and death.
Importantly, whether being infected with SARS-CoV-2 causes severe or critical clinical outcomes in a patient can be influenced by a number of factors.
Some of these are inherent in a patient, such as their age. Older age brackets, for example, have been associated with an increased risk of death.
Others are less so, such as whether a patient has previously been infected by the SARS-CoV-2 virus, or whether the patient has been vaccinated. Both of these factors have been associated with a decreased risk of severe outcomes.
And then there is the issue of the virulence] of the virus itself. That is, how severe are the clinical outcomes for a given strain, with all other factors being equal?
With a substantial proportion of Australia's total population still unvaccinated, whether or not the virus is less severe without the effect of vaccination is a pertinent question.
Mr Frydenberg's claim could convince someone who is vaccine hesitant, for example, to remain unvaccinated or not vaccinate someone in their care, if they interpreted Mr Frydenberg as speaking about the inherent virulence, absent the effect of a vaccine.
Fact Check takes Mr Frydenberg to be talking about this inherent virulence, rather than the effect of vaccination or previous infection on the severe outcomes of the virus.
The source of the claim
Fact Check contacted Mr Frydenberg's office to ask for the source of his claim.
A spokeswoman pointed to an opinion piece written by Doherty Institute director Sharon Lewin in the Sydney Morning Herald on January 2.
Professor Lewin compared the risk of hospitalisation between Omicron and Delta.
" … data from South Africa shows the risk of hospitalisation with Omicron compared with Delta is reduced by 80 per cent and, once in hospital, the risk of severe diseases with Omicron is reduced by 70 per cent." Professor Lewin wrote.
Mr Frydenberg's spokeswoman also directed Fact Check towards comments made by Chief Medical Officer Paul Kelly on December 31:
"Omicron, though, is less severe. I think that is becoming very clear now … There was a preprint paper that I read from South Africa. South Africa's a different country to in various ways, but they have had the longest and most extensive experience of this particular form of the COVID-19 virus, the Omicron variant. They are seeing a 73 per cent decrease in severity."
So which studies are Professor Lewin and Professor Kelly referring to?
South African studies
On December 21, 2021, a few weeks before Professor Lewin's opinion piece, researchers from South Africa's National Institute for Communicable Diseases published a pre-print, which was later published in peer-reviewed journal The Lancet on January 29, 2022.
The study used the lack of a certain gene, the S-gene, on the spike protein as a proxy to distinguish the Omicron infections. It referred to these as S-gene target failure, or SGTF, cases. At the time Omicron emerged in South Africa, the prevailing "non-SGTF" variant was Delta.
The study assessed comparative severity in two time periods. First, it looked at contemporaneous infections between October 1 and November 30, 2021. By the end of that period, the Omicron-proxy infections accounted for 98 per cent of infections.
Second, it compared SGTF infections in that period with genomically-sequenced Delta infections between April 1 and November 9, 2021.
The first analysis found an 80 per cent reduction in the risk of hospitalisation of SGTF infections relative to non-SGTF infections.
This analysis adjusted for a range of factors known to affect clinical outcomes for COVID-19 in South Africa, including age, sex, province, and health-care sector (private vs public) and known previous SARS-CoV-2 infection. But it could not adjust for the effects of vaccination status or comorbidities due to limited available data.
The second analysis found a 70 per cent reduction in severe disease with the Omicron variant relative to Delta in already hospitalised patients. Severe disease was defined as "a hospitalised patient meeting at least one of the following criteria: admitted to an intensive care unit; received oxygen treatment; was ventilated; received extracorporeal membrane oxygenation; had acute respiratory distress syndrome; or had died".
On top of other factors already mentioned, the analysis additionally adjusted for the effects of vaccination status and comorbidities.
The study's corresponding author, Nicole Wolter, of the Centre for Respiratory Diseases and Meningitis at the NICD, told Fact Check that reinfection status is generally under-reported and vaccination status was self-reported and only available for a subset of hospitalised patients in the study.
This, she said, meant the study could not fully adjust for these factors.
Furthermore, she said via email that the results of this study could be used to make comparisons between Omicron and Delta only.
"Our study found a reduced risk of hospitalisation/severity among Omicron compared to non-SGTF/Delta infections. This is likely due to a combination of high immunity in our population (from high numbers of previous infection and some vaccination), and potentially also reduced virulence of the Omicron variant," she said.
"From our study we are not able to disentangle the relative contribution of each of these factors, and cannot assign an overall magnitude as to how much less severe Omicron is relative to previous variants. We also did not compare Omicron to the ancestral strain, Alpha and Beta variants."
Which study was Professor Kelly referring to?
A spokeswoman for the Department of Health confirmed to Fact Check that Professor Kelly was relying on a different South African pre-print study.
This study analysed the beginning of three COVID-19 waves in Gauteng province which were dominated by different strains — Beta, Delta and Omicron, and is again from the NICD.
It found a reduction of 73 per cent in severe disease in the recent Omicron wave in hospitalised patients when compared to the Delta wave in the province, which is commensurate with the remarks made by Professor Kelly.
Severe disease was defined as "one or more of acute respiratory distress, supplemental oxygen, mechanical ventilation, high/intensive care or death".
The Beta wave was also analysed relative to the Delta wave, with only a 5 per cent reduction in the risk of severe disease, indicating similar severity profiles between Beta and Delta.
However, the study notes that its source, a national database called DATCOV, contains incomplete data on previous infection and vaccination, and therefore: "severely limits exploration of their potential roles in lower disease severity observed".
"This has meant that the role of vaccination could not readily be studied in relation to clinical severity of COVID-19," the authors wrote.
The authors recently updated their study, which was loaded to a different pre-print server, to include comparisons in severe disease of the Wuhan, Beta and Delta strains relative to Omicron, expanding the geographic area to include all of South Africa.
The updated analysis also included the entirety of the waves, rather than just analysing the beginning.
It found the risk of severe disease for those infected by Omicron relative to the original virus to be 52 per cent lower. The reductions relative to Beta and Delta were both around 72 per cent lower.
However, Fact Check has excluded this update to the study from its analysis, as it was not available at the time Mr Frydenberg made his claim.
Protection from vaccination or re-infection
These are not the only studies which have been done which compare the severity of variants of the SARS-CoV-2 virus.
Another pre-print wave analysis conducted in South Africa's Western Cape Province, which was conducted on behalf of the Western Cape and South African National Departments of Health, in conjunction with the NICD, also found a similar decrease in severe hospitalisation or death between Omicron and Delta waves.
However, this study also found that "severe COVID-19 outcomes were reduced mostly due to protection conferred by prior infection and/or vaccination" and that reduced virulence of Omicron may account for 25 per cent of the reduction in severe outcomes relative to Delta.
The study noted South Africa's "moderate" vaccine coverage in December 2021 ("39 per cent and 46 per cent of adults fully vaccinated in South Africa and the Western Cape respectively"), and said it was "important to establish whether protection against severe disease conferred by prior infection and/or vaccination is maintained against Omicron".
"Furthermore, to what extent does such protection account for milder clinical presentation of Omicron cases versus inherent differences in virulence of Omicron itself compared to previous variants? Such comparisons should not be limited to Delta, which was itself more severe than previous variants, and should fully account for the increased proportion of reinfections in an immune escape variant such as Omicron compared to other variants," the study said.
Further afield
Fact Check could find no academic research which attempted to quantify the severity of the Omicron variant relative to other variants in the Australian setting. But there are other analyses outside South Africa.
Another SGTF study in southern California. found a 52 per cent reduction in hospitalisation between Omicron and Delta.
Additionally, it found a 74 per cent reduction in the risk of ICU admission and a 91 per cent reduction in the risk of death.
It also cited the results of other studies in Scotland, the US and Canada, as well as two of the aforementioned South African studies mentioned in this fact check: "In other settings, estimated reductions in risk of hospitalisation with Omicron variant infection have ranged from 20-80 per cent".
"Variability in estimates between studies is likely in part due to different definitions of the primary endpoint (e.g. any attendance at hospital, admission to hospital, or admission to hospital with symptoms at the time of testing), differing lengths of follow-up, as well as varying levels of vaccination and prior infection across populations," the study said.
"However, these findings collectively suggest that differences in viral factors between the Omicron and the Delta variants, such as differences in viral tropism [the ability of a virus to infect a cell, tissue or host] or virulence factors, might be driving the observed relative reductions in disease severity."
Another non-peer-reviewed analysis was published by the Imperial College of London's MRC Centre for Infectious Disease Analysis.
The study used a combination of SGTF and genetic data to define Omicron and Delta infections from PCR-confirmed infections in England between December 1 and December 14, 2021.
It found the reduction in risk for Omicron relative to Delta was "40-45 per cent when using hospitalisation lasting 1 day or longer or hospitalisations with the ECDS [Emergency Care Data Set] discharge field recorded as ‘admitted' as the endpoint".
The study added: "However, assuming only 33 per cent of true reinfections are identified as such, corrected estimates suggest lower reduction in Omicron hospitalisation compared with Delta (ranging from approximately 0-30 per cent depending on the data subset) …"
A second analysis was also performed which stratified participants by vaccination and re-infection status.
This analysis found an unvaccinated individual infected with Omicron is 41 per cent less likely to be admitted to hospital relative to an unvaccinated individual whose primary infection is Delta.
Correcting for under-ascertainment of reinfections, this number fell to 24 per cent.
Other variants
As noted in the Western Cape, South Africa study, the Delta variant has been found to be more severe than other variants, which raises the issue of relative severity among multiple variants, and whether Mr Frydenberg is entitled to compare several variants to Omicron using a single figure.
This dynamic was noted by Raina McIntyre, head of the biosecurity program at the Kirby Institute, in an opinion piece for the Saturday Paper, in which she said: "Omicron may be half as deadly as Delta, but Delta was twice as deadly as the 2020 virus."
Indeed, a study in Singapore found Delta to be 1.88 times more likely to cause pneumonia compared to the ancestral strain after adjusting for age, sex, comorbidities and vaccination, but not reinfection.
Another in Scotland found Delta was associated with a 1.85 times increase in the risk of hospitalisation compared to the Alpha variant.
And the Western Cape study also found the first wave, dominated by the ancestral strain, and the second wave, dominated by the Beta strain, were 45 and 40 per cent less severe than the Delta wave respectively.
Catherine Bennett, the chair of epidemiology at Deakin University told Fact Check that it's not possible to lump together different strains under a single figure for severity.
"So the variable virulence, and the fact that this might also vary within sub-lineages and depending on the nature and extent of immunity in a population makes these types of general statements very hard to make," she said.
Angela Webster, a professor of clinical epidemiology at the University of Sydney's School of Public Health told Fact Check that comparisons between Omicron and previous variants other than Delta, as Mr Frydenberg has made, are made difficult by a range of different factors.
"Omicron makes younger people more symptomatic, but everyone seems to be less likely to need hospitalisation, but now we are so well vaccinated that might play into this too," she told Fact Check in an email.
"Comparing [the] impact of variants only really makes pragmatic sense with the one preceding — Omicron v Wuhan, when Wuhan isn't out there anymore? It's an exercise without meaning," she said.
Tony Blakely, the head of population interventions at the University of Melbourne's School of Population and Global Health agreed that previous variants had different severities, and would have different severities relative to Omicron.
He noted the confusing nature of this, surmising that it was "probably best … to refer back to Delta", adding that "we all struggle with this," in defence of the Treasurer.
Waasila Jassat, who is the corresponding author of the study which Professor Kelly referred to and is a public health specialist at the NICD, told Fact Check that "it is likely that lower severity is due to intrinsic lower virulence of Omicron and prior immunity".
"South Africa has high levels of prior infection and hybrid immunity from prior infection and vaccination. However many other countries with high vaccination coverage and possibly lower prior infection have also seen similarly lower rates of severity (Denmark, UK, US) so I would imagine Australia would have a similar picture," Dr Jassat told Fact Check in an email.
What the experts say
Professor Bennett said the Imperial College study was the most "sophisticated and robust" she had seen. She added:
"UK data is relevant to [Australia] given overall immunity levels are likely to be comparable and the similarity of vaccines used and effectiveness against serious illness, but we may be underestimating how serious the infection can still be for those who are still immunologically naive given unreported prior infection might have protected more in the UK."
She said that the 75 per cent figure came from national cabinet in the weeks before Mr Frydenberg's claim, and that it was based on the latest data, but "that is changing all the time as analysts try to get cleaner data, better documented cases so they can adjust for age, prior infection and vaccination status."
Professor Blakely said, however, that while this study, and others, are useful, they have a flaw:
"That is that Omicron is more likely to be asymptomatic or very mild. Thus the people who get into these studies are already selected differently [between Delta and Omicron]."
He said that if he had a "magic wand" which could conduct the perfect study of all patients infected with Delta and Omicron, rather than those just picked up by testing, the reduction in severity would likely be much higher.
Professor Webster said: "With evolved care, vaccination, and treatment interventions, and no health system overwhelm, the death rate has been lower with Omicron. The most interesting thing medically is that there is emerging resistance to sotrovimab — the most effective intervention to omicron in our battery — so things may change in this space if we lose a previously effective treatment."
"Similarly generalising from other settings is not always reliable — South Africa has a younger population, and has much lower vax coverage than e.g. Australia," she said.
And she noted that "severity" can be a nebulous term, with so many different clinical endpoints to consider.
"We still know little about Omicron in long Covid and other sequelae of infection. Persistent disability is of great importance to individuals and society and the media focus really hasn't turned to that much," she said.
Principal researcher: Online Editor Matt Martino
factcheck@rmit.edu.auSources
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