In less than a month, the new Covid variant has made it around the world – including to New Zealand. Siouxsie Wiles breaks down what you need to know about the rapid spread of omicron.

It’s hard to believe that it’s been only a few weeks since we first heard about the omicron variant. Since then it’s spread all around the world, including to Aotearoa. 

So, what do we now know about omicron?

It’s very transmissible, and cases are rising really fast

Dr Ridhwaan Suliman posted this graph on Twitter that compares cases in Gauteng, South Africa for each of their Covid waves. The red line is omicron. The rise in cases compared to the previous waves is astonishing. 

Similar rises are being seen all over the world, from Denmark and Germany to the UK and US. Cases are doubling every two to three days. A few days ago, 72% of positive PCR tests in London looked to be omicron. The UK was already experiencing a surge in delta cases, but that’s been swamped by omicron, which has become the dominant strain. Closer to home, New South Wales just announced they’d had 2,566 cases in the last 24 hours. A week ago, they were averaging about 500 cases a day.  

A couple of new lab studies give one potential reason for the increased transmissibility of omicron. In one, researchers from the LKS Faculty of Medicine at The University of Hong Kong looked at the ability of omicron and delta to infect and replicate in human lung and bronchial tissues. These tissues come from people who are having surgery or other medical procedures and would normally be discarded, but these researchers can keep them alive for a few hours to use them in experiments. 

The researchers found that omicron was 70 times better than delta at infecting and replicating in bronchial tissues and 10 times worse at infecting and replicating in lung tissue. The bronchi are the two large tubes that carry air from your windpipe to your lungs. What this means is that the omicron variant probably replicates better in the upper airways, so people may well be breathing out more virus particles. It remains to be seen whether replicating less in the lungs means the omicron variant will cause less severe disease. 

Meanwhile researchers from the US, Germany and South Africa showed that fake viruses (known as pseudoviruses) made to look like omicron were twice as infectious as delta in their lab-based experiments. All the data is pointing the same way.

Omicron and vaccines

Both that study using omicron pseudoviruses and a heap more lab-based studies have shown that the antibodies people make either after they’ve been infected with an earlier version of the virus or if they’ve received two doses of the Pfizer or other vaccines aren’t able to neutralise the omicron variant well, if at all. The picture looks better if you’ve had a booster. 

The numbers vary, but they all suggest that double-vaccinated people will be at much greater risk of catching omicron than they are of catching delta. Of course, there is lots more to our immune system than just antibodies, so these experiments can’t tell how well being vaccinated will protect against serious disease for those people who do test positive.

The findings of those lab studies are certainly playing out in the real world, with lots and lots of vaccinated people testing positive for omicron. Arrivals into our managed isolation system all have to be double-vaccinated and we’re already into double digits for omicron cases in just a few days. The virus also spread across the hall between two vaccinated people in a hotel managed quarantine facility in Hong Kong. There have also been some extraordinary super-spreader events including a party held at a restaurant in Oslo, Norway. As of a week or so ago, around 70 of the 120 party goers had tested positive. So had another 50 people who were at the restaurant at the same time. It sounds like all were vaccinated. 

Meanwhile, data from the UK is suggesting that two shots of the Pfizer vaccine is about 30-40% effective against omicron and a third dose boosts that to 70-80%.

Is disease with omicron milder?

It’s too soon to tell. Hospitalisations and deaths normally lag cases by several weeks as it takes time for people to get very sick, and sometimes they can be in intensive care for weeks to months before they die. 

There are two things we really need to know. How well do the vaccines protect against serious illness and death from omicron, and what happens to people who aren’t vaccinated who get omicron? Here in New Zealand, the overwhelming majority of our eligible population have had two doses of the Pfizer vaccine. But we do have some people who aren’t vaccinated. Or course, we also have all of our under 12s unvaccinated at the moment. The paediatric Pfizer vaccine has just got provisional approval from Medsafe, so hopefully will start being rolled out soon. But it will take time to get them all vaccinated. 

Here’s another graph tweeted by Dr Suliman showing hospitalisations are now on the rise in Gauteng. We’ll be watching to see what happens in other places.

Over the weekend, Imperial College London released an interim analysis of omicron cases in the UK. The study concluded there were at most limited changes in severity of disease between omicron and delta. But even if does turn out that omicron causes a milder illness for most people, that won’t be the case for everyone. And because of the sheer volume of people catching omicron, hospitals are still likely to be overwhelmed. Remember “flatten the curve“? Even a disease that is relatively mild for lots of people can still bring healthcare systems – especially those already battered by waves of Covid-19 – to their knees. We also don’t yet know whether those who have a mild illness from omicron will go on to develop long covid and be impacted for life. 

Let’s hope the incredible efforts of everyone working at our border will keep omicron out of the community for as long as possible, at least till we can get our children vaccinated and everyone else a third dose.