[LINK] COVID Pandemic Tradeoffs modelling

[Stephen Loosley]

2022 will be better:

COVID-19 Pandemic Tradeoffs modelling

September, 2021

This report may be cited as: Blakely, T., Wilson, T., Andrabi, H., Thompson, T. (2021).
“2021 will be better: COVID-19 Pandemic Tradeoffs Modelling.”
Population Interventions Unit, Melbourne School of Population and Global Health.

Corresponding author: Tony Blakely, ablakely at unimelb.edu.au

Ref: https://populationinterventions.science.unimelb.edu.au/pandemic-trade-offs-september-2021/
(This tool allows you to explore how COVID-19 policy responses (restrictions, vaccination roll-out, and border opening) impact future SARS-CoV-2 infection, hospitalisation and mortality rates, and the future probability of lockdowns.)

And quoted below:

Ref: https://populationinterventions.science.unimelb.edu.au/posts/pandemic-trade-offs-september-2021/2022-will-be-better_COVID-19-Tradeoffs-modelling-21-SEP.pdf


Modelling Summary

2022 will be better than 2021.

For us to ‘live with the virus’ will take more effort that what many of us assume, but by
effectively using the tools we have now and innovating, we can achieve a well-functioning
society in 2022.

A commonly held view is that we can ‘open up’ at 80% vaccination coverage of adults, in a
scenario we call the Default Scenario. In our modelling this is a loose suppression policy
designed to limit hospitalisations to a level that our health care system can handle. We
expect travel to increase to the point that, on average, after screening, one vaccinated but
infected person unwittingly crossing our borders undetected per day. The health loss of
this scenario is arguably tolerable, at about 4000 hospitalisations over the year (range 2300
to 7300) in a state the size of Victoria. But – in our COVID-19 Pandemic Tradeoffs modelling
at least – this default scenario requires us to spend more than half the year in lockdown.

We have to do better than this.

In an Upgraded Scenario that extends 80% vaccination coverage to include children (5+
year olds), and keeps moderate public health and social restrictions in place even when
case numbers are low (e.g. some density limits in hospitality), we will be ‘okay’.

‘Okay’ under this Upgraded Scenario actually looks pretty good in health loss terms with
a range of between 130 to 1800 hospitalisations from COVID-19 over the year, and 36 to
490 deaths. Not to belittle preventable deaths from infectious disease, these base scenario
estimates of mortality are about 5% to 50% of the deaths per year from influenza and
pneumonia in Victoria.

But the flipside of this contained health loss is the social cost to keep the pandemic under
control. Even for the Upgraded Scenario we might expect 14% of time is expected in some
form of lockdown, with a wide uncertainty range of 0% to 50% of the year in lockdown.
These scenarios only show us we can achieve in 2022 without stretching ourselves too
much. In fact, we can do better:

1. Increase vaccine coverage to 90%: Achieving 90% vaccination coverage of both children and
adults will slash the hospitalisation and death rates by about 80%, and we will most likely have no
time in lockdown at all (so long as we keep moderate public health and social measures in place at
all times).

2. Reducing overseas/interstate infected incursions: Reducing the expected number of
vaccinated but infected arrivals that get into our community undetected from 1 per day to 1 every
five days (equivalent to the current risk from 200 vaccinated quarantine-free arrivals per day from the
UK in a State the size of Victoria) achieves the same reductions in health loss and time in lockdown
as 90% vaccination.

These two improvements are for interventions we understand reasonably well. We also
need to innovate to reduce our reliance on lockdowns as the main tool to augment high
vaccine coverage. Our modelling suggests that improved air filtration and ventilation of
buildings (e.g. school rooms and office buildings), higher rates of mask use even when
we are not in lockdown, a third dose of an mRNA vaccine to all those double-dosed
with AstraZeneca, deployment of mass rapid antigen testing when we need to dampen
transmission without resorting to lockdowns, and technological enhancements to contact
tracing (e.g. Bluetooth enable apps that both work and satisfy privacy concerns) can all
have important impacts – reducing health loss, and reducing the need for lockdowns even
more.

It is critical to note that it is not the vaccination coverage alone that determines what
opening up and 2022 will be like. Rather, it is the full package of measures – of which
vaccination coverage is just one. Public and policy discourse should reflect this reality.
To achieve a better way of living in 2022, we also need to watch out for a few things.
There is convincing evidence emerging of substantial waning vaccine immunity for both
AstraZeneca and Pfizer to the Delta virus. We first need to complete the job of vaccinating
the global population. This is important for equity, and also because it reduces the chance
of a dangerous new variant emerging. But when we can, we will need to roll out third or
booster vaccines to everyone. Especially and first to recipients of AstraZeneca.

Assuming and hoping a more infectious, lethal and vaccine resistant variant of the virus
does not emerge, we should be optimistic that 2022 will be substantially better than both
2020 and 2021. We have choices as to what mix of measures we use to chart our way to and
through next year, including known interventions (vaccines, border controls, suppression
policies within country) and innovations we can see coming (ventilation, mass rapid
testing).

This report covers 432 possible scenarios, each modelled 100 times in an agent-based
model to capture as many futures as possible. All results are publicly available at an
interactive webtool, COVID-19 Pandemic Tradeoffs (www.pandemictradeoffs.com).

Our modelling finds that predictions are sensitive to two important and poorly understood
input parameters. First, the proportion of Delta infections that are asymptomatic. If in our
modelling we use the estimates used in the Doherty-led report, the situation deteriorates.
Second, there is genuine uncertainty about the effectiveness of current vaccines at reducing
onwards transmission if a vaccinated person is unlucky enough to become infected. In
our model we assume this reduction is 25% on average. If we replace this with the 65%
reduction assumed in the Doherty-led modelling, the situation improves dramatically.
However, we fear that the 65% reduction assumed in the Doherty-led report – based on
evidence accruing since their modelling – is too optimistic.

Pulling back, we all need to be cautious about the sensitivity of modelling predictions to
inputs we do not yet fully understand. We need to use modelling to plan our opening up,
then nimbly alter how we open up as actual data arrives in real-time.

Our modelling supports a key finding in the Doherty-led Report that keeping ‘light
restrictions’ as a minimum at all times dramatically reduces the need for lockdowns. We
concur that, unfortunately, allowing society to go back to near normal settings when case
numbers are low often allows transmission to gain hold, and requiring longer lockdowns
to bring surges back under control. As 2022 progresses, and we move into 2023, we can
probably ease these minimal restrictions as immunity from natural infection creeps up
and we revaccinate the whole population with better vaccines that (hopefully) reduce
transmission risk more than current versions.

Our modelling also extends on the Doherty-led modelling in important and policy-relevant
ways. For example, we do not start from a baseline of 30 infected cases, but account for
ongoing community transmission as Australia is experiencing now, and how case numbers
respond dynamically to restrictions and other measures. The time-window of our work
also extends beyond 6 months to the end of 2022, including the first year after opening up.

That is our modelling attempts to represent the patterns of infection growth and decline
we are likely to experience from now through 2022.

Melbourne School of Population and Global Health
September 2021