Crawford School of Public Policy

The New South Wales COVID-19 epidemic has highlighted the divisions in National Cabinet about what vaccination level needs to be reached before Australia can relax its COVID-19 restrictions, Dr Zoë Hyde, Professor Quentin Grafton, and Professor Tom Kompas write

On 30 July, National Cabinet’s National Plan to transition Australia’s National COVID-19 Response was announced, intended to manage a shift in Australia’s pandemic response from the suppression of COVID-19 to managing the virus like other common respiratory diseases.

As part of this plan, vaccination targets for those aged over 16 were set. These targets were informed by epidemiological modelling undertaken by the Doherty Institute and an economic impact analysis by the Australian Treasury.

Currently, Australia is in Phase A of the Plan, the ‘vaccinate, prepare and pilot’ phase, with the goal to “strongly suppress the virus for the purpose of minimising community transmission”.

Once 70 per cent of the adult population is fully vaccinated with two doses of vaccine, Australia will transition into Phase B, where the goal will be to “…to minimise serious illness, hospitalisation and fatality as a result of COVID-19 with low level restrictions”.

Phase C begins when 80 per cent of the adult population is fully vaccinated, and its goal will be “…to minimise serious illness, hospitalisations, and fatalities as a result of COVID-19 with baseline restrictions”. Phase C will only allow for highly targeted lockdowns.

Finally, Phase D’s goal is to “manage COVID-19 consistent with public health management of other infectious diseases”. This final phase of the Plan is likely to be reached in 2022. At that point, international borders will reopen and there will no longer be ongoing public health restrictions or lockdowns. In other words, COVID-19 will be managed like other common respiratory diseases, akin to treating the virus “like the flu”.

Unfortunately, this National Plan to transition Australia’s COVID-19 response is back to front. Instead, the Government should establish a transition strategy based on the following three key pillars.

First, it must be built on staying below a transparent and agreed-upon maximum tolerable number of hospitalisations and fatalities, as well as long COVID cases, determined by National Cabinet.

Second, it should identify the minimum vaccination level for the total population and for vulnerable groups required to achieve public health goals. These numbers should be fully informed by comprehensive risk analyses, account for scientific uncertainty in key parameters, and be comprehensible to decision-makers.

Third, it must evaluate public health and economic trade-offs – at different vaccination levels – for both the total population and vulnerable groups.

We have modelled the projected outcomes of dropping all public health measures and managing COVID-19 like the flu at different levels of vaccination.

Our modelling evaluates the effects of vaccinating children, providing a single mRNA booster (of Pfizer or Moderna vaccine) to all those who received the AstraZeneca vaccine, and vaccinating all those 60 years of age and older at a higher level than the general population – 95 per cent.

Our results are built on four key assumptions.

First, that when Australia no longer imposes adequate public health restrictions or lockdowns, everyone will eventually be exposed to the virus that causes COVID-19.

Second, we assume that Australians will face a variant that is at least as transmissible as the Delta variant, which has an estimated basic reproduction number, or R0, of six.

Third, that fatality rates will be at least as high as those observed for the original strain in 2020.

And finally, that vaccine effectiveness against infection, symptomatic disease, and hospitalisation are, respectively, for AstraZeneca: 60, 67, and 92 per cent, and for Pfizer: 79, 88, and 96 per cent.

Making these assumptions, our modelling shows that herd immunity against strains as contagious as the Delta variant can be achieved if 95 per cent or more of the entire population is vaccinated, but only if people who receive the AstraZeneca vaccine are subsequently given a mRNA booster shot.

We find that if 70 per cent of Australians over 16 years of age are fully vaccinated, but with a 95 per cent vaccination level for those aged 60 years and over, there could eventually be some 6.9 million symptomatic COVID-19 cases, 154,000 hospitalisations, and 29,000 fatalities. Notably, hospitalisations and fatalities would not be restricted to the unvaccinated.

Further, if just five per cent of symptomatic cases result in long COVID, where serious symptoms such as post-viral fatigue can persist for months or longer, and which can also occur in vaccine breakthrough infections, some 270,000 Australians could develop long COVID, even if 80 per cent of those aged 16 years and over are vaccinated.

If children are also fully vaccinated, national fatalities – for all age groups – would be reduced to 19,000, assuming 80 per cent adult vaccination coverage, and would fall to 10,000 at a 90 per cent adult vaccination coverage.

Children also benefit directly from vaccination. Our projections indicate that 12,000 hospitalisations could be prevented in children and adolescents if 75 per cent vaccination coverage is achieved in these age groups.

Giving adults a booster dose of an mRNA vaccine further improves outcomes. At 80 per cent adult vaccination coverage but allowing for an mRNA booster for all those fully vaccinated with AstraZeneca, symptomatic cases, hospitalisations, and fatalities could be much less, with our modelling predicting 6,000 fewer deaths.

Our projections of fatalities are much higher than those of the Doherty Institute used in the National Plan. The Doherty Institute, relative to our modelling, assumed: a shorter modelling time horizon, a lower assumed proportion of symptomatic infections, lower transmission among children, baseline public health measures that reduce the reproduction number from 6.32 to 3.6, and that Test, Trace, Isolate and Quarantine remains partially effective, even at very high new daily cases.

Our projections of hospitalisations and fatalities would have been even worse if we had used the higher preliminary estimates of the increased virulence of the Delta variant. This means our projections likely represent a lower estimate of the cumulative public health outcomes of fully relaxing public health measures at Phase D of the National Plan, or sooner, if outbreaks are not effectively suppressed or eliminated.

Our results suggest that four key vaccination steps must be followed before exposing Australians to uncontrolled SARS-CoV-2 infection.

First, children and adolescents should be vaccinated.

Second, vaccine coverage among adults aged older than 60, and in other vulnerable groups like among Aboriginal and Torres Strait Islander Australians, should be 95 per cent or higher.

Third, Australians vaccinated with AstraZeneca should be given an mRNA (Pfizer or Moderna) booster before the international border reopens or public health measures are prematurely relaxed when there is ongoing community transmission. Those vaccinated with an mRNA vaccine should also receive a booster shot, when appropriate.

And, finally, Australia needs very high vaccination coverage for the entire population, preferably more than 90 per cent, to mitigate excess deaths.

If the country achieves these four steps, fully relaxing public health measures to eliminate community transmission could still, eventually, result in some 5,000 fatalities and 40,000 cases of long COVID.

By comparison, under the National Plan, assuming 80 per cent vaccination coverage overall for those over 16 – without attaining 95 per cent coverage in those aged 60 and over – there could be 10 times as many cumulative fatalities, approximately 50,000, and some 270,000 cases of long COVID, when public health restrictions are fully relaxed.

The consequences of prematurely relaxing public health measures to suppress COVID-19, even after vaccinating 80 per cent of adults, would likely be irreversible, and unacceptable to many Australians.

National Cabinet must not squander its opportunity to devise a safe and affordable transition to a ‘post-COVID-19’ era. If National Cabinet revises its strategy to include our four vaccination steps, many lives will be saved, and many more (including children) will not suffer from debilitating long COVID.

The information contained in this article is not formal medical advice regarding COVID-19. For individual medical advice about COVID-19 and COVID-19 vaccinations, consult with your GP.