University of Newcastle health experts, who have examined the latest research, say vaccines remain a crucial tool in dealing with the virus. But the findings into the effectiveness of one antiviral have been much less promising.

The former Morrison government strongly promoted antiviral drugs, amid the push to end COVID restrictions earlier this year.

The government listed the antiviral drug molnupiravir, sold by Merck under the brand name Lagevrio, on the PBS in March.

It is one of the two antiviral medications that the federal government approved to treat COVID. The other is the Pfizer drug Paxlovid.

Molnupiravir was found in a major UK study to be no better than a placebo at lowering the risks of death and hospital admission.

It remains available in Australia to everyone over 70 and people aged 50 years and older with two or more risk factors for severe disease, along with immunocompromised people.

Professor Joshua Davis, a John Hunter Hospital infectious diseases specialist, said the results of the University of Oxford's Panoramic trial was a "big news story".

"It's a big deal because the Australian government purchased a huge amount of that drug [300,000 courses]," Professor Davis said.

"Basically the trial showed it really has no benefit in preventing hospital admissions or mortality," he said.

Pharmaceutical company Merck defended Lagevrio, saying a separate study in Israel found the drug reduced hospitalisations and mortality in high-risk patients 65 years and over.

Nonetheless, as is standard in the pharmaceutical sector, Merck funded the studies that led to the drug being approved.

Merck said in October last year that the pill could halve the chances of dying or being hospitalised for those most at risk of contracting severe COVID-19. It revised that in December, saying the drug only reduced hospitalisation and death by 30 per cent, not 50 per cent.

The United States had ordered 3.1 million doses of the drug for $2.2 billion by November last year, but France cancelled its order for the antiviral drug in December.

"The first half of the trial showed good effects. That was the interim analysis. On the strength of that, it got approved in Australia," Professor Davis said.

Merck projected sales of the drug would amount to $5 billion to $6 billion this year.

Professor Davis said it's a "huge story if it turns out this drug does nothing and someone has made billions."

The Panoramic trial did show the duration of symptoms for people who took the drug was four days less than those who received ordinary care.

"My take on the whole thing is I never thought it would be a very effective drug," Professor Davis said.

He said the people who took the drug in the trial knew they were receiving it, so it could have worked as a placebo in regards to the duration of symptoms.

"There's a lot of debate about that now," he said.

"My take is the drug probably does nothing, but we can't say that for sure."

Professor Davis said the dominance of Omicron and a highly vaccinated population meant "the disease is much less severe than it was even a year ago".

"For me that's one of the main takeaways from that trial. It means it's going to be really hard to show any drug is effective because the disease is so mild," he said.

Asked if vaccines were still needed if the disease is mild, he said: "Vaccination is still really important".

"One of the reasons why the disease is now so mild is because most of the population is vaccinated.

"And most of the population have also had COVID. Both of those things together really boost your immunity."

He said a vaccination program should continue.

"I think if we all suddenly just stopped getting boosters now, it'd be fine for six or 12 months but next year we'd see a big wave of more severe disease," he said.

The University of Oxford's Panoramic trial is also testing the other approved antiviral drug, Paxlovid.

The results of that are expected in the next couple of months. The former Morrison government ordered 1 million courses of Paxlovid.

Associate Professor Nathan Bartlett said the virus had evolved and "we have to think about how that would impact the way an antiviral might work".

"We should be clear that the Panoramic study hasn't been peer-reviewed," said Dr Bartlett, a virologist with University of Newcastle.

"It found that those who were on the drug had some positive effects. People recovered more quickly, about four days faster, which is quite significant.

"And they shed less virus, which means they were less infectious to others."

Dr Bartlett said Omicron doesn't attack the lungs as aggressively as previous variants like Delta.

"So if you're dying from Omicron, it's probably a combination of your response to the virus interacting with some other pre-existing disease."

So reducing the amount of virus - with the antivirals - may not make a difference in that scenario.

"Even if you reduce the amount of virus by half, it may already be too late. All the antivirals are doing is reducing the amount of virus."

This is why the antivirals are recommended to be taken in the first week.

"You'll always have a subset of people with whom the antivirals won't do much because the virus has been there long enough to trigger the events that will lead to them getting very sick."

Furthermore, he said antivirals are difficult to develop for respiratory viruses.

"The viruses get in the airways quickly and start replicating," he said.

"Getting those antivirals early enough is always going to be the challenge."

He said the world had "mostly relied on vaccines" to deal with COVID.

"Protection is better than treatment - get in before the virus arrives. But I'm sure we'll see advances in antivirals as we move on."

Professor Peter Wark said the "biggest thing with the antivirals is that the original studies were done on populations that were unvaccinated".

"They were also done on variants of the virus, predominantly Alpha and Delta," said Professor Wark, a senior staff specialist in respiratory medicine at John Hunter Hospital. "In fairness, they are more aggressive viruses in many ways."

The original trials of the two drugs showed the data was "a bit stronger for Paxlovid, as opposed to molnupiravir".

"Paxlovid is probably at this stage more effective than molnupiravir, but the jury is still out on that.

"But also you have a population that is vaccinated now and Omicron is milder.

"So people are less likely to end up with bad outcomes such as hospitalisation or death anyway."

He said the antivirals would have "very limited role if any" in people under 65 who don't have a significant comorbidity.

"If you're previously well and you're vaccinated, you'll get better without the antivirals. You don't need them. If you're immunosuppressed and the vaccine is not going to work, that's a different matter."

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