Passing 10,000 Omicron cases in a day is a warning to hit the brakes

The Omicron strain of COVID-19 is clearly more infectious than Delta. Witness NSW crashing through 10,000 cases in a 24- hour period, Victoria approaching 4000 cases a day, South Australia running as high per capita rates as Victoria, and Queensland gaining momentum.

Thankfully, Omicron is less severe in its impact on health than Delta – somewhere between 10 per cent to 50 per cent of the hospitalisation rate for notified cases.

Melburnians wear face masks as they shop at the Queen Victoria Market.Credit: Getty Images

With Delta, we expect something like 350 to 500 people in hospital on any given day following an announcement of 1000 new cases about two weeks prior. With Omicron, we are heading to something like 100 people in hospital on any given day for 1000 daily cases two weeks earlier.

This ratio worsens if Omicron infects older people more than it has in Britain. Conversely, it will improve as we boost people rapidly – especially older and vulnerable people. The ratio may be lower than 100 from 1000 if people hospitalised with Omicron have less severe disease with shorter lengths of stay – which seems likely based on overseas data so far. Improved treatments that prevent or shorten the length of hospital stay should – with widespread boosting – drive the ratio lower again. But we cannot count on that just yet.

But – as many have said – less severity does not necessarily mean less pressure on the health services because Omicron spreads so much more easily.

NSW has hit 11,201 cases notifications per day which (presuming Delta is now largely replaced by Omicron) should result in about 1000 people in hospital on any given day in two weeks or so.

That is probably as much as NSW health services would like to cope with, so there is an urgent need to “hit the brakes” with density limits and encourage people to stay at home – now.

‘Do we let case numbers run at a high level - say about 10,000 a day in a state the size of NSW or Victoria?’

Moreover, there is momentum that will take time to turn around, meaning a peak of 20,000-plus cases a day (and somewhere around 2000 people in hospital on any given day) is not unrealistic. Which is more than the NSW health systems would like to be managing.

The NSW situation is a wake-up call to other states (if it was needed) to dab the brakes now: we can support mask mandates, speed up boosters as much as possible, impose density limits, work from home, limit our socialising on holidays, ensure better ventilation indoors, and all the other measures we are now used to.

Plus, more rapid procurement of rapid antigen tests and the strategic use of mass rapid antigen testing. Hopefully, these measures will be quick enough and sufficient, and we help avoid lockdowns, but that is not guaranteed.

That is what we are looking at in the next few weeks. But what about after that? Do we aim to keep moderate to strong restrictions in place until case numbers are driven low again (e.g. fewer than 1000 cases a day), or do we loosen restrictions early and let case numbers run at a high level (say about 10,000 a day in a state the size of NSW or Victoria)?

There will be many inputs to this decision, including social and economic considerations. But let’s think about the “things we need to know” from a health perspective to rationally inform this decision.

If we get clear signals from vaccine producers that new vaccines are coming mid-2022 that are not only better at preventing serious illness, but also greatly reduce transmission, then it would be rational to drive case numbers back down again (if we can), minimise caseloads, and wait for these better vaccines to get us out of this pandemic.

However, if much better vaccines do not appear forthcoming, there may be merit in allowing moderate to high case numbers of Omicron to continue.

First, if everyone is going to be exposed to COVID-19 at some point (which seems likely), then it would make sense for those who refuse to get vaccinated to take their chances with Omicron; the next variant may be more virulent again.

Second, we really want to know (or at least have a reasonable prediction of) how common long COVID is after an Omicron infection. To me, at least, I suspect that Omicron will induce long COVID less frequently and less severely. Why? Because it is more an infection of the airways, not the “body”. But my conjecture is just that – conjecture that needs other experts to weigh in on. In parallel, we need to examine what early data we can lay our hands on.

Third, we want to know what immunity an infection with Omicron induces against future variants. This is obviously impossible to know definitively until the next variant hits. But we do want some working idea now. My reading of existing studies on pre-Omicron variants is that an infection does boost immunity and is better than vaccination at preventing future infection – which is necessary to try to stop COVID-19 just reinfecting the population again and again. I assume this will apply to Omicron, and perhaps even more so given it is more an infection of the upper airways. But we need virologists, immunologists and other experts to estimate as best they can what scenarios are most likely.

These “known unknowns” are important to make reasonable predictions upon which to make the best choice for how we live with Omicron (and variants after that) in 2022. It is, essentially, a choice between ongoing suppression versus moving to allow COVID-19 to become more endemic – with natural infection boosting vaccine-induced immunity to make us more resilient in the future.

Professor Tony Blakely is an epidemiologist and public health medicine specialist at the University of Melbourne.

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