What comes after Omicron?

Omicron has dominated Covid-19 cases since it was detected last November, but scientists say it's unlikely to be the last variant we grapple with.

So what's likely to come next? And will our current vaccines work for it?

The truth is that no-one knows what the future holds - but scientists around Australia are already preparing for the unknown.

What could the next variant after Omicron look like?

For another variant to become dominant, it will need to have certain features which allow it to out-compete Omicron.

This could mean being more transmissible or being better at evading existing immunity, said Megan Steain, a virologist and senior lecturer with the University of Sydney.

"If it can't do both those things, it can't out-compete what's currently circulating ... that tells us it's going to have to have a specific combination of mutations," she said.

But as to whether a new variant will be more severe or have worse symptoms? Dr Steain said that's the "million dollar question".

"There's no way to know, really," she said.

"I would like to think that as the level of general immunity across the globe increases just through vaccination and infection, that that basic level of immunity would still mean that we're less likely to have more severe disease by future variants, but it's by no means guaranteed."

Edward Holmes, an evolutionary biologist and virologist from the University of Sydney, also said there was no guarantee the virus would become less severe over time.

In fact, until Omicron, SARS-CoV-2 had increased in severity as it evolved: Alpha was more virulent than the original Wuhan variant, and Delta was more virulent than Alpha.

Omicron was less likely to cause severe disease than Delta, but Professor Holmes said Omicron's more recent subvariants, BA.4 and BA.5, could be more virulent than its earlier BA.1-3 subvariants.

"The virus cannot increase its virulence and transmissibility forever: at some point changes in these characteristics will start to impinge on other aspects of virus biology," he said.

"But unfortunately it is not possible to say when that point will be reached.

"All we can do is try to get the highest vaccine coverage we can - globally, not just in rich western countries - and encourage people to wear face masks to reduce transmission. Then we just watch and wait."

The only safe prediction, according to Professor Holmes, is that the virus will keep evolving and never leave us.

Where will the next variant of concern come from?

Even for scientists, it's another tough one to predict.

Dr Steain pointed out that when Delta was dominating, it was so prevalent many scientists assumed the next variant would be some kind of Delta derivative.

And yet, along came Omicron - a new, highly transmissible variant with a bunch of strange mutations that hadn't come from Delta.

While Omicron was detected in South Africa, scientists are still trying to figure out how exactly it came about.

All viruses mutate over time, but SARS-CoV-2 has changed so much and so quickly that it's shocked many scientists.

"The virus circulating now is a very different beast to that first described in Wuhan at the end of 2019: it is more virulent and far more infectious," Professor Holmes said.

"If it wasn't for the rapid development of vaccines the human death toll would be in the tens of millions.

"It is therefore foolish to make strong predictions about what will happen next."

There are some theories about where the next variant could come from.

They include mutating from Omicron, emerging from a region where genomic surveillance is very low, or even spreading into animals then back into humans, Dr Steain said.

Will future vaccines work against the next variant?

With all this uncertainty it might seem difficult to combat whatever Covid throws up next, but scientists are on the case.

Even though all vaccines in use in Australia target the original Wuhan strain, they still reduce the chance of severe disease and death from all variants.

Moderna and Pfizer are both developing vaccines that target Omicron, which could be available in Australia by the end of the year.

Many researchers are also making progress on "variant-proof" vaccines that aim to protect against Omicron and other variants that emerge down the track.

Jennifer Juno, an immunologist at the Peter Doherty Institute in Melbourne, where three vaccine candidates are in different stages of development, said there were different ways to boost protection.

"Sometimes we might want to say to the immune system, 'Just focus on this part of the virus here. This is the part that has the biggest changes'," Dr Juno said.

"Or we might need to show parts of the virus to the immune system in a slightly different way than what it saw before, or maybe we give different doses or things like that.

"All of our vaccines are trying to understand how we can maximise the immune response to a new variant, generally in individuals who have already received a vaccine that targeted the first form of the virus."

Jamie Triccas, a professor of medical microbiology at the University of Sydney, is the lead investigator on a project with Dr Steain looking at developing a vaccine with a modified spike antigen.

"The hope is that there will be a breadth of immune responses that's generated by the vaccine we developed that will give some level of protection against a new variant that emerges," he said.

"It's very hard to predict what will come along, so you're really just trying to improve your chances of giving a level of protection."

Experts say people who aren't up to date with existing booster shots should do that first to get the best protection possible, rather than waiting for future vaccines.

Vaccines have to go through a rigourous testing process before they can be released to the public. It's for good reason - to make sure they are safe and effective - but it does mean it can take some time to finalise a candidate.

Amid the uncertainty, the good news is that the pandemic has seen the global scientific community work together like never before, and that's expected to continue.

"I hope in the future that some of the interest that we have in mucosal vaccines or pan-coronavirus vaccines pans out and brings some new products to the landscape," Dr Juno said.

- ABC