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COVID-19 chart updated with Omicron risk of death, benefits of boosters

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Since the rise in COVID infection rates with the spread of the highly infectious Omicron variant, the need to get booster doses in arms has becoming more pressing.
 
Based on the nationally applied four-month interval, the Department of Health told newsGP that as of 25 January approximately 10,678,000 people are currently eligible for a booster, which is likely to be higher given the interval has dropped to three months in a number of states.
 
The latest data, however, as of 23 January shows just over 6.5 million people aged 18 and over have received more than two doses, suggesting millions of Australians are currently in need of a booster.
 
With GPs expected to once again be in the position of explaining the benefits of vaccination, the Immunisation Coalition has updated its COVID-19 Risks Chart to include more data on the benefits of boosters.
 
As more people who received AstraZeneca as their primary dosing schedule become eligible, the chart now includes expanded insight on the risk of death based on timing since vaccination with AstraZeneca, as well as the benefits of a booster dose of either Pfizer or Moderna.
 
The risk assessment has also been updated to include data on the Omicron variant, with scenarios based on 90% of transmission of Omicron and 10% Delta to reflect the current reality in Australia.
 
Professor Colleen Lau, an NHMRC Fellow and Professorial Research Fellow at the University of Queensland School of Public Health, told newsGP she developed the chart with GPs in mind in the hope of making the most of limited consultation time.
 
‘Using this chart, you can show a patient what level of protection they would have at various time periods after the second dose,’ she said.
 
‘The main messages in this chart are firstly to show that vaccines work and secondly, you can see that vaccine effectiveness wanes over time after the second dose and … your chances of dying increases.
 
‘Once you get your booster that risk dramatically reduces, so it’s really important to get the booster as soon as people are eligible, particularly the older age groups because they are definitely at higher risk.’
 
To make it as easy to use as possible, the matrix has been designed using the same formatting and colour coding system as the Absolute Cardiovascular Risk Calculator, with risks outlined by gender and different age cohorts, from 12 through to 70 and over.
 
It includes the risk of death for those who: 

• are unvaccinated
• have received one dose of either AstraZeneca or Pfizer three weeks ago
• two doses less than two months ago
• two doses 2–4 months ago
• two doses 4–6 months ago
• have received a booster of either Pfizer or Moderna two months ago.

For example, the risk of death in the current transmission scenario for a female aged 60–69 who is unvaccinated is estimated to be 22 per 10,000. Two doses of AstraZeneca in the last 2–4 months reduces that risk to six deaths per 10,000. However, once the timeframe since the second dose increases to 4–6 months, the risk increases to 10 per 10,000.
 
In the instance that the patient receives a booster, that risk drops significantly to 1.4 deaths per 10,000 – a marked improvement from two doses alone.
 
The benefits of a booster are even greater for those aged 70 and over.


Protection afforded by the AstraZeneca vaccine wanes after to 4–6 months. (Image: AAP) 

For an unvaccinated male in this cohort, the estimated risk of death from Omicron is 362 per 10,000. That risk drops to 74 within two months of receiving the second dose of AstraZeneca, but rises to 134 at 4–6 months.
 
A booster dose with either mRNA vaccine reduces the risk of death to 18 per 10,000.
 
Impact of Omicron
While Omicron has been branded by some as a ‘milder’ variant, the high transmission rate and ability to cause breakthrough infections means the seven-day moving average for daily deaths is currently more than three times higher than it has been at any other point during the pandemic – despite Australia’s high vaccination rates.
 
Professor Lau said the public’s perception of this may mean GPs find themselves having to argue the benefits of vaccination, which is where she hopes the chart will make that job a little easier.
 
‘Some people might think that vaccines are not working, as they hear that even vaccinated people can die,’ she said. ‘That’s true, as you can see on the chart vaccinated people can die, but the chances are much lower.’
 
A caveat of the chart is that it is based on population-level data and does not take into account individual comorbidities, with the risk of death for people with serious medical problems likely to be higher.
 
And while older cohorts are at greater risk of death, Professor Lau says when discussing the benefits of boosters it is important to consider other potential complications from infection, such as passing on the virus to vulnerable people and developing long COVID, even for younger patients.
 
‘While this chart is just about chances of dying, a lot of young people do feel quite sick even with Omicron infection,’ she said.
 
‘When they say Omicron is mild, it mostly refers to the fact that most people don’t need to be in hospital or ICU, but people can still feel really unwell.
 
‘And when you have so many people infected you can still overwhelm health systems, overwhelm GP clinics, overwhelm hospitals – as we’re seeing right now. So it’s not just your chances of dying that you need to think about.’
 
The chart has been developed as a tool that can be used either on its own or alongside the Immunisation Coalition’s COVID-19 Risk Calculator (CoRiCal), a collaboration with UQ, Queensland University of Technology, and Flinders University.
 
The team is currently in the process of updating the online calculator with the latest data from the chart, which is expected to be released next week. 
 
In the meantime, there are plans to include risks based on various comorbidities and for a similar online tool focusing on children aged 12 and under.
 
However, Professor Lau says that lower rates of PCR testing and challenges related to obtaining rapid antigen tests means there are uncertainties around the accuracy of data that is emerging.
 
‘We don’t know what the true case numbers are, which means that it’s difficult to work out what the true case fatality is because we don’t know what the denominator is,’ she said.
 
‘So this is based on the data that we have available and it’s fairly consistent with international data in terms of your chances of dying from Omicron if you’re unvaccinated, but as more data become available, we’ll update the tool as well.’
 
The COVID-19 Risk Calculator (CoRiCal) can be accessed on the Immunisation Coalition website. The COVID-19 Risk Chart based on the risk of Delta is also available for download, with the updated chart on Omicron expected sometime this week.
 
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