Doherty Institute COVID-19 modelling - Key findings and implications 3 August 2021
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Doherty Institute
COVID-19 modelling
Key findings and implications
3 August 2021
0
Doherty modelling provides evidence to update the 4 phases of the
National Plan to transition Australia’s National COVID-19 Response
On 2 July 2021, the Government released the National Plan to transition Australia’s National COVID-19 Response
(‘National Plan’). On 29 July, the Doherty Institute provided its final report and health modelling.
The Doherty Institute’s modelling suggests the National Plan be updated, taking into account the Delta
SARS-CoV-2 as a more transmissible variant and updates on vaccine effectiveness.
The key changes include:
Vaccine thresholds have been identified that may facilitate the transition to Phase B and Phase C of the
National Plan. The public health measures to support the different Phases have also been reviewed
and updated.
There is an emphasis on maintaining high vaccination rates across Phases by offering all adults a
vaccine earlier.
In Phase B and Phase C, ongoing low-level or baseline restrictions and effective test, trace, isolate and
quarantine (TTIQ) capabilities should be used to minimise cases in the community.
The experience with the Delta variant has shown with an outbreak under Phase A, lockdowns should
be early, stringent and short.
.
1As of 30 July 2021
National Plan to transition Australia’s National COVID-19 Response
National Cabinet agreed to formulate a national plan to transition Australia’s National COVID-19 Response from its current pre vaccination settings, focussing on continued suppression of
community transmission, to post vaccination settings focussed on prevention of serious illness, hospitalisation and fatality, and the public health management of other infectious diseases
Phases triggered in a jurisdiction when the average vaccination rates across the nation have reached the threshold and that rate is achieved in a jurisdiction expressed as a
percentage of the eligible population (16+), based on the scientific modelling conducted for the COVID-19 Risk Analysis and Response Task Force
~70% vaccination ≥80% vaccination
(2 doses) (2 doses)
A. Current Phase: C. Vaccination Consolidation D. Final
B. Vaccination Transition Phase
Vaccinate, Prepare and Pilot* Phase Post-Vaccination Phase
Continue to strongly suppress the virus for Seek to minimise serious illness, Seek to minimise serious illness, Manage COVID-19 consistent with
the purpose of minimising community hospitalisation and fatality as a result of hospitalisations and fatalities as a result public health management of other
transmission COVID-19 with low level restrictions of COVID-19 with baseline restrictions infectious diseases
Measures may include: Measures may include: Measures may include: Measures may include:
Accelerate vaccination rates; Open international borders;
Maintain high vaccination rates, encouraging Maximise vaccination coverage;
Close international borders to keep COVID-19 out; Quarantine for high-risk inbound travel;
uptake through incentives and other measures; Minimum ongoing baseline restrictions,
Early, stringent and short lockdowns if outbreaks
Minimise cases in the community through adjusted to minimise cases without lockdowns; Minimise cases in the community without
occur;
ongoing low-level restrictions and effective Highly targeted lockdowns only; ongoing restrictions or lockdowns;
Minimise cases in the community through effective
track and trace; Live with COVID-19: management
test, trace and isolate capabilities; Continue vaccine booster programme;
Implement the national vaccination plan to offer every Lockdowns less likely but possible; consistent with influenza or other infectious
Exempt vaccinated residents from all domestic diseases;
Australian an opportunity to be vaccinated with the International border caps and low-level
restrictions;
necessary doses of the relevant vaccine as soon as international arrivals, with safe and Boosters as necessary;
proportionate quarantine to minimise the risk of Abolish caps on returning vaccinated Allow uncapped inbound arrivals for all
possible;
COVID entering; Australians; vaccinated persons, without quarantine;
Inbound passenger caps temporarily reduced;
Ease restrictions on vaccinated residents Allow increased capped entry of student, and
Domestic travel restrictions directly proportionate to economic, and humanitarian visa holders;
(TBD); Allow uncapped arrivals of non-vaccinated
lockdown requirements;
Restore inbound passenger caps at previous Lift all restrictions on outbound travel for travellers subject to pre-flight and on arrival
Commonwealth to facilitate increased commercial levels for unvaccinated returning travellers and vaccinated Australians; testing.
flights to increase international repatriations to Darwin larger caps for vaccinated returning travellers; Extend travel bubble for unrestricted travel to
for quarantine at the Centre for National Resilience in
Allow capped entry of student and economic new candidate countries (Singapore, Pacific);
Howard Springs;
visa holders subject to quarantine and
International Freight Assistance Mechanism extended; arrangements and availability; Gradual reopening of inward and outward
Trial and pilot the introduction of alternative quarantine Introduce new reduced quarantine international travel, with safe countries and
options, including home quarantine for returning arrangements for vaccinated residents; and proportionate quarantine and reduced
vaccinated travellers; requirements for fully vaccinated inbound
Prepare/implement vaccine booster
Expand commercial trials for limited entry of student programme (depending on timing). travellers.
and economic visa holders;
Recognise and adopt the existing digital Medicare
Vaccination Certificate (automatically generated for
every vaccination registered on AIR);
Establish digital vaccination authentication at
international borders; * No jurisdiction required to increase restrictions beyond current settings
Prepare vaccine booster programme; and The Plan is based on the current situation and is subject to change if required
Undertake a further review of the national hotel The COVID-19 Risk Analysis and Response Taskforce’s report will be available once finalised at: pmc.gov.au.
quarantine network. 2
4The Doherty Institute modelling indicates that vaccinating around 70%
of the population aged 16+ may allow Australia to transition to Phase B
of Australia’s National COVID-19 Response
Vaccination coverage is a continuum, with every increase reducing transmission and negative health outcomes.
Younger adults are peak transmitters of COVID-19, while older adults experience the most severe health impacts.
As supply allows, extending eligibility to all adults (16+) offers the greatest potential to slow down transmission.
Once around 70% of the population aged 16 and over is vaccinated, Australia may be able to move to Phase B of the
National Plan without exceeding health system capacity, so long as this is combined with effective test, trace, isolate
and quarantine and low-levels of ongoing restrictions and public health measures, including:
Social distancing and capacity
Maintaining effective track and
limits in commercial settings
trace, isolation and quarantine
and workplaces
2sqm social distancing (or Record keeping and
density restrictions) COVID-safe plans
In Phase B, lockdowns are unlikely with low levels of ongoing restrictions.
3At 70% vaccination coverage, the number of strict lockdowns would be
significantly reduced
Percentage of time needed to stay in strict lockdowns with
optimal test, trace, isolate and quarantine measures and
low-level restriction measures
40%
Rapid epidemic growth and high caseloads are
expected at 50% and 60% coverage of the 30%
population, with more substantial transmission
reduction at 70% and 80%. 20%
10%
Therefore, until we have high vaccination
coverage: 0%
Any outbreaks are likely to have rapid 50% 60% 70% 80%
and uncontrolled growth, with Vaccine population coverage
significant morbidity and mortality and
requiring regular and extended All adults allocation strategy
lockdowns.
With vaccine coverage around 70%, strict lockdowns will be
The optimal strategy is likely to be to unlikely. Low case numbers can be maintained with light
continue with the suppression approach restrictions which ensures test, trace, isolate, quarantine
and lock down early and hard when measures are most effective.
there is an outbreak to limit the
duration and costs of lockdowns. It is not possible to constrain an outbreak in Phase B using light
restrictions when vaccine coverage is only 50% or 60%.
The Federal Government will align its economic Differential vaccine rates by age group will be necessary to
support and assistance to support faster and minimise severe health outcomes and transmission.
stronger lockdowns in Commonwealth-declared
COVID-19 hotspots while we are in the suppression The vaccination rates of those over 60 is expected to be
phase. around 90% by the time there is movement to Phase C.
4As vaccine coverage increases, less stringent public health and social
measures will be required to bring transmission potential below 1
The chart below shows the combined effects of vaccination and public health and social measure scenarios on COVID-19
transmission potential under the ‘All adults’ vaccination scenario assuming optimal TTIQ effectiveness, due to high
caseloads. Standard age (60+) and dosing interval (12 weeks) recommendations are assumed for AstraZeneca.
Original strains (Wuhan)
could be suppressed
Non-VOC R0
without vaccination
Transmission potential (TP) is
the average number of
secondary infections produced
by a typical infection case.
TTIQ capacity
Track, Trace,
is critical
5At 70% and 80% vaccination coverage, the rates of severe infections are
greatly reduced in an uncontrolled outbreak scenario
Cumulative symptomatic infections
over the first 180 days of an outbreak These charts are likely to overstate the
(‘All adults’ vaccine allocation strategy) numbers of infections and deaths. The
numbers would be significantly lower with
low level restrictions and effective TTIQ.
80%
The modelled scenario is premised on the
70% seeding of infections by 30 individuals. The
scenario is unlikely as it assumes baseline
60% restrictions (minimal density and capacity
restrictions).
50%
0 200,000 400,000 600,000 800,000 1,000,000
No hospitalisation Severe cases Severe infections
(‘All adults’ vaccine allocation strategy)
Deaths, ≈1,000
80%
The modelling ≈1,500
70%
assumes vaccine coverage Even coverage is
is uniform across Australia. critical and could be
≈4,100
However, outbreaks could assisted by monitoring 60%
quickly spread through and heat maps to
sub-groups with lower identify local 50% ≈6,800
rates of vaccination. government areas that
need greater support to 0 10,000 20,000 30,000 40,000 50,000 60,000
raise their vaccine uptake. Ward admissions ICU admissions Deaths
6As supply allows, extending vaccinations for adults under 40 years offers
the greatest potential to reduce transmission now that a high
proportion of vulnerable Australians are vaccinated
Age-based transmission matrix
Vaccine uptake by young
adults (age 16 and over) will
strongly influence the
impact of vaccination on
overall transmission
Why this works
Younger adults (15-24 years), followed by adults of working
Cumulative symptomatic infections over the first 180 days
age, are peak transmitters of COVID-19 due to high social
by vaccination coverage and allocation strategy
mixing.
1,200,000
(cumulative over 180 days)
Symptomatic infections
1,000,000
800,000
600,000
400,000
200,000
0
50% 60% 70% 80%
Population vaccination thresholds
Allocation strategy: 'Oldest first' 'All adults'
7Outcomes for a difficult to control outbreak vary under different
vaccination strategies
The table below shows the cumulative symptomatic infections, ward admissions, ICU
admissions and deaths over the first 180 days for the coverage threshold of 70% achieved
by the ‘Oldest first’ strategy compared to the ‘All Adults’ strategy*
Age Group This table is likely to overstate the
numbers of infections and deaths.An addendum to the modelling found that a ‘transmission reducing’
vaccine allocation strategy is marginally better than an ‘all adults’ strategy
The table below shows the cumulative symptomatic infections, ward admissions, ICU
admissions and deaths over the first 180 days for the coverage threshold of 70% achieved
by the ‘All Adults’ strategy compared to the ‘Transmission reducing’ strategy*
Age Group
This table is likely to overstate the
numbers of infections and deaths.The addendum report found ongoing low level restrictions and optimal
TTIQ could improve outcomes around 100 fold or more
The table below shows the cumulative symptomatic infections, ward admissions, ICU admissions and deaths over
the first 180 days for the coverage threshold of 70% achieved by a ‘transmission reducing’ vaccine allocation
strategy with optimally effective TTIQ and ongoing low level restrictions compared to partially effective TTIQ
and ongoing baseline restrictions
Age GroupWe need to increase the uptake of AstraZeneca to combat the
challenge the aggressive Delta strain presents to Australia
Vaccine effectiveness estimates (% reduction)
Pfizer BNT AstraZeneca
The Delta strain has intensified the need for increased 1 dose 2 doses 1 dose 2 doses
vaccination uptake globally.
Symptomatic
33% 83% 33% 61%
Full AstraZeneca vaccine coverage is comparable to full infection
Pfizer coverage in reducing death and hospitalisation, and
health advice recommends adults under the age of 60 Hospitalisation 71% 87% 69% 86%
should consider getting AstraZeneca.
ICU admission 71% 87% 69% 86%
Given current supply, there are positive outcomes from
an increased uptake of the AstraZeneca vaccine among
Mortality 71% 92% 69% 90%
people aged 40 and over.
The table above shows two doses of the AstraZeneca vaccine are
More than 750 million AstraZeneca vaccines have been comparable to two doses of Pfizer for reducing hospitalisation, ICU
supplied globally in the past 12 months. In the United admission and death.
Kingdom, 24.7 million first doses and 22.8 million
second doses have been administered as of 14 July 2021.
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