Experts fear with the UK suffering "two epidemics on top of each other", there's an increased likelihood Omicron and Delta could swap genes, making them potentially even more dangerous.
The UK is experiencing its biggest wave of the pandemic yet. While the number of Brits infected with the Delta variant of the SARS-CoV-2 virus is stable, the highly infectious Omicron variant is spreading rapidly. Data suggests it's already dominant in London, and could see hundreds of thousands testing positive a day as soon as Christmas.
While most viral evolution occurs due to replication errors, they do have the ability to mix their genetic material with other viruses in a process called 'recombination'. This can happen when they infect a host call at the same time.
Speaking to the UK Parliament's science and technology committee this week, Moderna chief medical officer Paul Burton said it was "certainly" possible Omicron and Delta could team up in this way and create a more dangerous strain.
"There's certainly data, there have been some papers published again from South Africa earlier from the pandemic when people - and certainly immunocompromised people - can harbour both viruses," he said, according to UK media reports.
"That would be possible here, particularly given the number of infections that we were seeing."
It was estimated on Wednesday about a fifth of all cases in the UK were Omicron, but that's rapidly increasing. At present most parts of the UK have a single dominant strain, reducing the likelihood they'll bump into each other inside a cell - but it's growing more likely the worse the outbreak gets.
Kiwi genomics scientist Mike Bunce of the Institute of Environmental Science and Research said recombination could result in a mutant combo virus with the worst of both strains.
"Using genomics, there remains a lot of scrutiny of Omicron and Delta including the possibility of the variants 'merging'… which can occur if infected with both variants at the same time."
Scientists told the MailOnline previous known recombinant events in the COVID-19 pandemic haven't created strains that were able to beat Alpha and Delta. But there's evidence Omicron itself is the result of such an event.
Virologist Sarah Palmer of Sydney's Westmead Institute recently said Omicron bears hallmarks of being the result of the Alpha and Delta strains sharing genes.
"We're very, very concerned," she told ABC.
"It indicates that possibly we could see that variants can recombine, and if somebody is infected with two variants there could be a recombination that could lead to a more pathogenic and infectious virus."
Sequencing has found Omicron is less related to Delta than it is to Alpha, the variant that was first discovered in the UK in late 2020. But it's a few times more infectious than Delta, which is about 50 percent more infectious than Alpha.
"The genomics of Omicron came as a surprise to many working in the field as it looks as if the Alpha variant went into hiding (for about 12 months) and then reappeared with a new game plan," said Dr Bunce.
Omicron was first picked up in southern Africa, which has the world's highest rate of HIV - a virus that weakens the immune system, increasing the potential for multiple viruses to infect a person at once.
A similar theory holds that Omicron's extreme ability to infect people stems from a genetic sequence it has that isn't in any other strain of SARS-CoV-2 - and might have pinched from a coronavirus that causes the common cold virus.
The scientist behind that theory has sought to play down suggestions that could be why Omicron's symptoms appear to be milder than previous variants. It's unclear at this stage whether Omicron is actually a less virulent strain, or the immunity offered by vaccines and prior infections is making it appear that way.
But it hardly matters when it's so infectious, said Dr Bunce.
"Even if Omicron or another variant result in half the hospitalisation rate, twice as many infections will place the same net demand on the hospital system."
New Zealand reported its first case of Omicron in managed isolation and quarantine on Thursday.
