Omicron – just when you thought the end might be in sight

Dr Norman Swan looks at what we currently know about Omicron.

Omicron has been declared a variant of interest by the World Health Organisation, and a lot has happened since. 

From a variant we had not heard about just a few days ago, it has now spread around the world to over 40 countries.

There are three big questions: 

  • Does it escape immunity that we have if you’ve been infected before or if you’ve been vaccinated?
  • Is it better at spreading than Delta? 
  • And does it matter? Is the disease worse, milder, the same than what we’ve seen before with previous variants of coronavirus? 

So, let’s start at the beginning. How effective is immunity?

There is a preprint, and that means that it’s a non-peer-reviewed paper, that has come out of South Africa, looking at 2.7 million people who have been infected with SARS-CoV-2, the COVID-19 virus, prior to the end of August 2021. So, they’ve been largely infected during the periods of the Wuhan virus, the Beta in South Africa, and the Delta, and then they looked at the rate of reinfections in the same group three months after the first one.

What they are finding is that Omicron has escaped immunity to a significant extent, and it’s about 2.4 times more likely to produce a reinfection in somebody who has got a prior immunity compared to wave one, so in other words the first wave with the ancestral virus. So, there is antibody escape.  

What we don’t know at the time of writing what this means for people who’ve been vaccinated.  

Anecdotally it looks as though you can be infected but the vaccines are still ok at preventing serious disease

So, what about how contagious Omicron is compared to Delta or previous variants?

Again, we know the most information from South Africa, which is a very different population. Prior to Omicron, South Africa had their lowest level of COVID-19 that they had ever had in the pandemic. And then it’s gone from about 300 cases on average a week to about 5,000 rolling average at the time of writing, and it’s gone from a 1% positivity rate to about 35% positivity rate in the Gauteng Province.

You’ve got to tie this in to reinfection because this virus doesn’t actually have to be a lot more contagious than the Delta virus to see a significant surge, because if this virus has escaped immunity to a significant extent, as that study suggested, then the population to the virus looks as though it’s non-immune. So you’ve got a vulnerable population into which it can go, irrespective of whether they’ve been infected before, and perhaps irrespective of whether they have been vaccinated before, and that could cause your surge, pretty much all on its own, if it is just as contagious as Delta. That’s another thing that we don’t know yet.

How do we interpret what’s happening there in an Australian context?

That’s an important question for us. We are not that different from the South African population because a very high proportion of people have had COVID-19 or been immunised. In Australia not many of us have had the infection, but a large percentage of us have been immunised, and quite recently, which means that we’ve got a reasonable level of antibodies. So, it’s too early to say, but it could mean that if it gets in, it would still spread, which really brings us to the third question, how much does it really matter? Is it a worse disease?

At the time of writing there is not much evidence either way. Comforting evidence from South Africa which is that people seem to be in hospital for fewer days than they did with earlier variants, but that could just be a function of previous immunity, not necessarily the mildness of the virus. It could simply be because it’s moving into a population that has experienced COVID-19 before, either through vaccination or through previous infection, and therefore when you get infected with this virus, you don’t get as severe disease. So, it’s not a feature of the virus, it’s a feature of us and our immunity.

But there are some worrying signs. There’s a spike in admissions of 0- to 4-year-olds in Johannesburg and that’s not well explained. Part of it might be that they are doing COVID testing on kids who are already in hospital for some other reason. Part of it may be a genuine spike in 0- to 4-year-olds, but that is a bit worrying at the moment, at our level of ignorance.

As to vaccination, it’s still going to be protective against serious disease but we need as high a level of immunity as possible, so it was mildly surprising that they did not change the advice about boosters in Australia. We are still waiting to 6 months and there have been reports that some providers are running the risk of throwing out vaccines and yet people are coming forward for earlier boosters. In addition, Moderna still hasn’t been approved as a booster.  

Internationally people are saying, well, you really want to get these boosters in so that the antibody response is as high as it can be, so you’ve got the strongest immunity both in antibodies and the T cell response, as we can possibly get.

The good news is that the Therapeutic Goods Administration has approved provisionally Pfizer for 5- to 11-year-olds, which I suspect will be very welcome for many parents. 

myDr
Author: myDr

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