19 Dec 2021

Prof Gary McLean on the rise and (eventual) fall of Omicron

From Sunday Morning, 8:19 am on 19 December 2021

We may think we have a handle on the Omicron variant, but are we sure? People are certainly being hospitalised, and some are dying, albeit thankfully in low numbers. Dr Gary McLean is a Professor in molecular immunology at London Metropolitan University and a researcher with Imperial College. He's an international authority on coronaviruses. He joins Sunday Morning for the final time this year to discuss the Omicron variant.

Gary McLean

Gary McLean Photo: Supplied

We're only just beginning to learn more about Omicron, but how sure are we of what we do know so far? People are certainly being hospitalised, and some are dying, though thankfully in low numbers.

Dr Angelique Coetzee in South Africa, the woman who alerted the world to this Covid-19 variant, has said Omicron is largely causing "mild disease", and there's no need to hospitalise people with mild cases of Omicron. So why is there so much global consternation?

Omicron may be mild in South Africa, but that's not what the UK is seeing.  Modelling has suggested the UK could see 24,000 coronavirus deaths by April, even with boosters. And WHO Covid-19 spokesman Dr David Nabarro said he's never been so concerned during the pandemic.

"No doubt this variant has got a big advantage in transmission, it's spreading very fast, we know that," McLean told Jim Mora.

"Since the alert in late November it's been found in 89 countries, [there's] probably many more to come, it's spreading faster than any variant so far, as far as SARS-CoV-2 has. We had yesterday, here in the UK 15,000 confirmed cases by sequencing - and likely the number is much much higher than that because not all of them are sequenced to that level."

The fact Omicron had overtaken Delta in parts of the UK showed how quickly it was spreading, with 80 percent of new cases in the UK now thought to be Omicron, he said.

"The numbers here are going up really fast... the last three days were breaking pandemic records, 78,000, 88,000 93,000 [daily cases].  Omicron is thought to double every one-and-a half to three days, and we've also got Delta still rumbling along, and that's contributing too.

"As far as clinical severity caused by Omicron the best estimates come out of South Africa, because they've had it in circulation for longer.  Possibly it looks more mild, slightly less severe disease, but that could reflect their population demographic - it's younger, they've also got a bit of prior immunity, because they had the Beta outbreaks a while ago, and the vaccines together."

McLean said it was too early to know if Omicron was a more mild disease or not, but he is optimistic it might be.

"However, if we just look at hospitalisations, they're increasing in South Africa and here in the UK as well, and most of those people ending up in hospital are unvaccinated ...it's a bit of a mixed bag, it's not looking great to be honest."

Research into Omicron to date is still too small and too early to give a good wide picture, McLean stresses that so far it offers only clues, not a full picture of how Omicron will behave.

"We just still don't know essentially."

What is clear, however, is the risk posed by its rapid spread.

The UK Health Security Agency has said so far Omicron has an Rt number of 3.7 in the UK. That's: "the reproduction number of the virus", McLean said, "the average number of new infections from one person.  

"So that would mean on average 3.7 people get infected from one, and then those 3.7 people can go on to infect 3.7 more. If it's over 1 the epidemic is growing."

A Hong Kong University study of both Delta and Omicron's effects on different types of body cells in the laboratory found that Omicron multiplies 70 times faster in one day than Delta does in the bronchus cells, the middle airways.

"That could match with increased transmission of the virus," McLean said.

"Interestingly, the infection rates in the lungs was much much lower than Delta - so that suggests that Omicron might not infect the lungs quite so well." This could be a reason for less severe disease - if that does prove to be the case, he said. However he warned the study's findings are limited by the fact it was carried out on isolated cells in a laboratory, and the findings should be interpreted carefully.

He said while it was inevitable the Omicron variant would eventually cross the border into New Zealand's wider population, its arrival here should be slower "because there'll be fewer entry points."

"Once inside though... it'll take over from Delta and case numbers will go up, unless you put other control measures in place.

"I think keeping it out for as long as possible while building up vaccine immunity is the way forward for New Zealand."

Vaccinations versus Omicron

Different sources vary widely on whether vaccine top ups are desirable, or on how vaccinations are holding up against the new variant.

"Omicron is spreading in countries with good vaccination rates, so that doesn't look good," McLean said.

Early studies indicate those who have both recovered from previously being infected with Covid-19, and also been vaccinated could have the best immunity against Omicron.

He said Pfizer's recent advice that top-ups of the vaccine are desirable is more likely to reflect the real situation as they data represents 'real world' cases.

"I think that boosters are going to be super-important here, they're going to give people enhanced immunity that lasts, and can deal with this Omicron wave."

He explained that people who've had two doses of the vaccine have an immune system 'memory' which allows their body to recognise the virus as a threat and respond to fight it.  But, a booster shot rallies the immune system again to be more alert, so that if the virus shows up it can respond faster and with more force.

A healthcare worker conducts a PCR Covid-19 test at the Lancet laboratory in Johannesburg on November 30, 2021 as a new, heavily mutated Covid-19 variant, dubbed omicron, spread across the globe.

A healthcare worker takes a sample to test for Omicron, at a research laboratory in Johannesburg, South Africa, on 30 November. Photo: AFP or licensors

A German laboratory study has found the structure of Omicron's spike proteins are different enough to previous variants that some medicines designed to latch onto the virus's spikes may not be as effective.

"I think the monoclonal antibody therapies are going to struggle with Omicron. The antivirals themselves... target different parts of the virus, so I think they'll be okay still, but with any kind of antiviral and RNA virus resistance will develop with time and use."

Body fat acts as reservoir, study suggests

A new Stanford study has suggested body fat acts as a reservoir for Covid-19 infection.

It showed that fat cells can be infected, as well as "pro-inflammatory" cells in fat tissue, McLean said. "So all of this can enhance the undesirable inflammatory response," and create more severe disease.

"The more fat cells you've got - the more obese if you like - the more chance for infection of those cells, and then the increased inflammation, and then the disease that comes from that."

McLean said coronaviruses have the ability to form new mash-up variants, so there is the possibility of two different Covid-19 variants combining - a step called recombination.

This could happen if two variants exist together in the same person and the variants come into contact in the same cell. They can swap chunks of their RNA genetic material, which could result in more significant structural differences in the new variant produced - creating a significantly different mutant variety.

"It's likely to happen - there's a chance, but it's quite rare. What we're seeing now mostly is the variants are point mutations - so single mutations, rather than these big recombination events. But it's entirely possible."

As it stands however, Omicron itself is going to take us on a rough ride, he said.

"Omicron is changing things currently... I suspect the rise is ... going to be be really fast and quite possibly the fall, the drop in case numbers ... is going to be equally fast as well.

"We've got the vaccines, we've got the boosters, we've got more knowledge, I think we can ride it out without extreme lockdown measures. ...I hope the virus is going to [reduce in effect] over time even though the infections are [increasing].

"What we've got to do is get more people vaccinated around the world, and give less chance for new variants to arise over time, and we'll get out of this."

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