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How important is Pfizer’s new COVID-19 antiviral likely to be?
The US pharmaceutical company has said clinical trial results of its new COVID-19 pill are ‘game-changing’. Experts give newsGP their take on its likely impact.
Paxlovid reportedly has an 89% efficacy rate at preventing hospitalisation among high-risk COVID-19 patients. (Image: AAP)
Results from a clinical trial of Pfizer’s new antiviral COVID-19 treatment have been released by the company, indicating a high level of protection against severe illness and death.
The treatment, known as Paxlovid, has an 89% efficacy rate at preventing hospitalisation among high-risk COVID-19 patients, according to details published by the company over the weekend.
With 500,000 courses of the oral antiviral already on order from the Federal Government, the drug could be prescribed by general practice in Australia if it is approved, as now seems likely.
Pfizer says that subject to authorisation, Paxlovid ‘could be prescribed as an at-home treatment to help reduce illness severity, hospitalisations, and deaths, as well as reduce the probability of infection following exposure, among adults’.
Peter White, a professor of microbiology at UNSW, told newsGP that the drug would probably be used outside of primary care initially if it is approved in Australia – but that general practice is likely to be involved at some point.
‘Down the track, if people go to their GP and they’re positive for coronavirus with symptoms, it’s very possible the GP will prescribe this drug for a few weeks to drive the viral load down,’ Professor White said.
Promising results
The Pfizer trial results were detailed in a company press release but have not yet been peer reviewed.
The study was randomised and double-blind, and began in July this year, the announcement says. Its results are based on the outcomes of 1219 adults with laboratory-confirmed cases of the virus, whose condition was monitored for 28 days after taking a five-day course of either Paxlovid or a placebo.
All those participating in the trial had at least one underlying health condition signalling a greater chance of severe illness and were treated within five days of the onset of symptoms.
Of those who received the Paxlovid course, six out of 607 were hospitalised, while there were 41 hospitalisations among the placebo group, which had a total of 612 individuals. There were no deaths reported in the group receiving the trial drug, compared to 10 in the placebo group, while the trial also suggested a good safety profile.
Pfizer has ceased planned further studies ‘due to the overwhelming efficacy’ shown in the results, with the company CEO Albert Bourla describing them as a ‘real game-changer in the global efforts to halt the devastation of this pandemic’.
However, while University of Queensland infectious diseases physician and microbiologist Associate Professor Paul Griffin said the news is welcome, he offered a more circumspect assessment.
‘It is a big step forward, but I would be cautious to use terms like “game-changer”,’ he told newsGP.
‘It’s clear the vaccination is still going to be the main intervention that underpins our management here. And as we have always said, prevention is better than cure.
‘This will certainly [improve] our ability to live with this virus. We’re fortunate to have a number of different options.
‘I think all those options will still have a use depending on the situation, whether it’s monoclonal antibody therapy, or the other antivirals.
‘Perhaps they may even be a combination of all those things at some point in time, as we get more evidence and understand exactly how they work potentially together.’
The high costs of antiviral treatment have also been highlighted, including by Professor Peter Doherty.
Like Associate Professor Griffin, he suggests vaccination remains the main line of defence against the virus.
‘These [antivirals] are not yet available and we don’t know when they will be in doctors’ clinics or when they will be approved for use,’ Professor Doherty said on social media. ‘They are also very expensive. Get the vaccine!’
Associate Professor Griffin also indicated the number of pills the company is able to produce will influence how useful the drug proves to be.
‘I’d expect that the accessibility, the scaling up, and manufacturing will improve, that costs will hopefully come down in time,’ he said.
‘All those things have to happen before it’s really going to be something that’s as widespread as we’d potentially like it to be.’
The pills are designed to be taken early in the onset of the disease for the greatest impact, and are taken alongside protease inhibitor
ritonavir. Last month, the Department of Health (DoH) announced it
had ordered enough pills for 500,000 courses, subject to its approval by the Therapeutic Goods Administration (TGA).
More antivirals to come
The DoH announcement followed Merck’s publication of its own COVID-19 antiviral drug trials. The treatment, molnupiravir (sold as Lagevrio), has now been
approved for use by UK regulatory authorities, the first country in the world to take the step.
Known domestically as MSD Australia, US-based Merck released results last month suggesting molnupiravir, which has been adapted to treat COVID-19 after
initially being developed as an influenza treatment, halves the risk of severe illness.
Much like Pfizer trial, nobody died after receiving the drug, although clinical trials suggest it has less impact in preventing hospitalisation.
While the two trials have been put aside each other, with Pfizer results interpreted more favourably in some quarters, Associate Professor Griffin said it is too early to reach any conclusions.
‘It’s very hard to draw comparisons between those two trials,’ he said. ‘Both of them were essentially halted early due to overwhelming efficacy. The numbers are still relatively small.’
Professor White also said more data is needed but believes Pfizer’s deliberate targeting of SARS-CoV-2 might give the treatment an advantage.
‘If you had to get me to choose which one I would like the most based on what they are and how they’re made, I would prefer the protease inhibitor because it’s actually targeting the viral enzyme called coronavirus,’ he said.
Professor White added that the number of antiviral pills on offer is likely to expand rapidly over the next two years.
The DoH has
300,000 of MSD Australia’s molnupiravir pills on order, again subject to their approval by the TGA.
Pfizer in the meantime said trials are also underway to assess its drug’s impact on ‘standard’ risk COVID-19 patients, and to evaluate its effectiveness as a prophylactic for those exposed to the virus.
The company said the data from the trial in high-risk patients will be used in a submission to the US Food and Drugs Administration for its emergency-use approval.
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