A "uniquely Australian" mix of variants will make treating severe COVID-19 more challenging, according to new research, with fewer drugs left in the "cupboard" that are effective against new strains of the virus.
A new paper spearheaded by the Kirby Institute in Sydney looked at 15 COVID-19 variants in circulation in Australia in 2022, and how successful two types of monoclonal antibodies — Evusheld and Sotrovimab — were in offering protection.
Monoclonal antibodies are a key tool doctors use to treat severe COVID-19, and are particularly important for severely immunocompromised patients or people who cannot get vaccinated.
The drugs were given either via injection or infusion to Australian adults, pregnant women and children who were at risk of developing severe disease.
The research, which has not yet been peer-reviewed, found Evusheld was ineffective against all variants tested.
Sotrovimab still provided some protection against most of the variants currently in circulation, but at a slightly lower level of effectiveness.
Kirby Institute researcher Stuart Turville, a co-author on the study, said the evasiveness of newer Omicron variants meant there were fewer effective treatments for people who were immunocompromised.
"It's taking [it] out of the therapeutic cupboard … cocktail antibodies and antibodies that have worked very well," he said.
"At the end of the day … what's left in the therapeutic cupboard is Sotrovimab, depending on the variant, but also Paxlovid [an antiviral]."
Newer variants better able to evade treatments
Monoclonal antibodies were once hailed as a scientific breakthrough in the effective treatment for COVID-19 patients at risk of developing severe disease.
Former US president Donald Trump was successfully treated with a monoclonal antibody cocktail when he got infected back in 2020.
The treatment's molecules work by binding to the SARS-Cov-2's virus's spike protein, neutralising the virus and helping prevent an infection from becoming severe.
But as the virus has mutated and evolved, so too has its spike proteins — meaning some monoclonal antibodies are less likely to be able to "bind" to newer variants.
Unlike previous years in the pandemic where new variants of concern would quickly dominate globally, Australia now has a mix of variants which is "uniquely Australian", Dr Turville said.
And while there are many different variants circulating now, one thing they all have in common are spike protein mutations that make them better able to evade antibodies.
Treatments need to 'continue to evolve'
Researchers said the large number of variants in circulation would make treating severe COVID-19 more challenging going forward.
"It's a reminder that we still need to be looking at this virus carefully in the context of therapeutic development. We still need to be looking at this virus carefully in terms of vaccination," Dr Turville said.
"And they're the two main arsenals in our cupboard, so to speak, that can reduce what we refer to as the viral load.
"I think reducing the viral load either by vaccination in the general community, reducing the viral load of people that are vulnerable are the key measures that we have to deal with this virus at the moment."
The research showed the variants most likely to evade monoclonal antibodies were BQ.1.1, XBB.1, BR.2.1 and XBF.
Only a very small number of cases of XBB.1.5, which is circulating in high numbers in the United States, have been detected in Australia.
While vaccines are less effective at stopping people getting infected with newer variants of COVID-19, the research found being fully vaccinated still offered protection against severe disease and death.
Infectious diseases physician and researcher Paul Griffin said the research highlights how treatments need to continue evolving in line with the virus's evolution.
He also said a number of antivirals, which work differently to monoclonal antibodies, were still effective at treating COVID-19.
"So Paxlovid as well as Lagevrio and Remdesivir, are all antivirals that we can use to reduce the burden of this infection," he told ABC News Channel.
"Part of the reason we're in such a good position is we do have tools like antivirals, but this highlights, they do need to continue to evolve as well."
Evusheld and Sotrovimab are the only monoclonal antibodies TGA-approved for use in Australia.
Editor's note 10/01/2023: A previous headline on this story said new variants pose challenges for "antiviral treatments", instead of "monoclonal antibody treatments". This error has been fixed.
