Against a surging Omicron adept at immune escapism, boosters and masks are Australia’s best weapons
Living with Covid has taken on a whole new meaning in 2022.
We had been prepared for the virus remaining in our communities, but Omicron has taken this to a different level. This is what “vaccine-escape” looks like.
As we watched the Delta outbreaks in New South Wales and Victoria slowly come under control in 2021 with the rise in the number of people completing our primary course of vaccination, we had every reason to be optimistic for some relief over summer, even with international and state borders opening.
But this was dashed with the arrival of Omicron before the year was even over.
Omicron took off in South Africa, where first reported, then progressively made its way around the world, peaking in Australia on 14 January this year. It was worryingly capable of establishing vast waves quickly wherever it landed, and not just because it was intrinsically more adept at spreading. It is most successful because of its ability to evade our immunity.
Neither prior infection nor vaccination provides much protection from infection with this variant. This is immune escapism, which comes from being physically different enough from other variants that our immune system doesn’t immediately recognise them to mount an attack, and Omicron represents a bigger step change than we saw in the previous immune escape creep with Delta – so much so some are arguing Omicron should not be lumped together with the other Sars-CoV-2 variants seen in this pandemic at all.
Immune escape undermines the immune system’s ability to ward off an infection, but thankfully we still have enough cross immunity from vaccination, infection, or both, to reduce our risk of serious illness. In the peak last January, we had more than 50 times the infections reported in the Delta wave, but only one-third more people in ICU.
What is even more quirky about this Omicron variant, and all its subvariant spinoffs, is that an Omicron infection does boost our immunity against coronavirus infection, just not against Omicron. You are less likely to get Delta after an Omicron infection, but reinfection with Omicron is still on the cards, especially with the succession of new subvariants that have followed BA.1.
This means Omicron can keep holding the pandemic centre stage, not just by being more transmissible, but by actively elbowing out other variants.
On the upside, this might also be knocking out other potentially nasty mutant variants that never get a foothold. But it is the ability to cause reinfections, even in those who have had a recent infection, that keeps Omicron infection rates high, creating the long outbreak we have seen persist from the day it landed on our shores.
With the arrival of Omicron, the booster vaccine dose suddenly became important for all of us.
It not only protected against waning
immunity, but the booster also elicits a different type of immune response than the first paired doses. Remarkably, it not only boosts protection from serious illness back up to the levels seen with Delta, it also, at least for a short time, restores some protection from infection, reducing infection rates by 40% or so for the first couple of months.
Not as good as the impact on controlling the Delta outbreak, but not bad now we are in the shadow of the next looming BA.5 subvariant peak.
This different infection world we find ourselves in now is the same challenge faced across the globe. We were ahead for a while in current infection rates as the northern hemisphere went into summer, and are currently sitting behind France, New Zealand and Singapore. We drop to 16th in the world when we look at the latest data on new death reports per capita, behind European countries still in summer.
We also only have half the daily death rate of New Zealand.
Australia’s death rate has climbed with successive Omicron waves, and we are not yet back up to the peak rate of three deaths per million we saw then. Other countries in their last winter when the first Omicron wave hit saw death rates between four and 18 per million.
We are doing comparatively well, despite having our own turn now at facing Omicron in winter.
We are also nowhere near the total death reports per capita seen across the globe, clustering with Singapore, Taiwan and New Zealand among the few countries that have less than 400 deaths per million population.
Canada is over 1,000, France and UK over 2,000, and the US has seen in total over 3,000 deaths among every million Americans.
This doesn’t make the news that we have now had more than 10,000 Covid-19 deaths in Australia any easier, but apply the statistics from these other countries to our population size and it reaffirms the lives we have also saved.
If we matched Canada or Denmark’s death rates, we would have had nearly 30,000 Covid-19 deaths in Australia by now, 45,000 with German rates, or 70,000 with UK.
The Sweden death rate translates to nearly 50,000 total deaths in a population the size of Australia, yet many still hold this up as some sort of template of success.
So, what does come next?
Well, if everyone eligible for a booster went out and had it tomorrow, we might keep a lid on the BA.5 wave. If those at more risk of serious illness all had their winter dose, we would also see less people ending up in hospital as infection rates rise.
There are no guarantees that you can prevent infection, and we are now exposed most places we go, especially in larger cities. But reducing risk might be the difference between having an exposure and having an infection. Or between having one infection, or multiple.
There are between 600 and 900 active cases reported per 100,000 people in Victoria now, and you can double or triple that to have an idea of what the actual infection rates likely are. That’s between 1 and 2% of the population.
Some will isolate, some will not, and many will not even know they are infected.
In NSW, new reported cases in the last four weeks exceed 100 per thousand in metropolitan Sydney, and 50 in many regional areas. That’s between 5 and 10% of these populations who have reported a recent infection, which likely translates to up to a quarter of the population.
Masks, boosters and general precautions won’t stop Omicron, but will reduce our risk of reinfection and help us get through winter.
Antivirals are also an important secondary prevention step for those who are infected and are at risk of serious illnesses. If we can keep a lid on infections and reduce the risk of disease escalation in the vulnerable, we will be able to undermine Omicron’s main weapon, reinfection.
Catherine Bennett is chair in epidemiology at Deakin University
Reducing risk might be the difference between having an exposure and having an infection