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From today, the RECOVERY Trial – the world’s largest study investigating potential treatments for severe COVID-19 – will begin testing the antiviral treatment Paxlovid.

Paxlovid, an oral antiviral treatment developed by Pfizer, is a combination of nirmatrelvir and ritonavir. Nirmatrelvir inhibits an enzyme that is critical for the replication of the virus that causes COVID-19, whilst ritonavir increases the concentration of nirmatrelvir.

Whilst Paxlovid has already been approved in the UK for treating patients with early-stage COVID-19 who are at high risk of developing severe disease (for instance, cancer patients), it is not known whether it can also benefit patients who have been hospitalised with COVID-19.

Sir Peter Horby, Professor of Emerging Infectious Diseases in the Nuffield Department of Medicine, University of Oxford, and Joint Chief Investigator for RECOVERY, said: ‘Two years into the pandemic, we are still lacking effective antiviral drugs for patients with severe COVID-19. Paxlovid is a promising oral antiviral drug but we don’t know if it can improve survival of patients with severe COVID-19.  By testing Paxlovid in RECOVERY we will find out.’

Dr Leon Peto, Senior Clinical Research Fellow for RECOVERY at Oxford Population Health, said: ‘RECOVERY has shown that antiviral antibodies that bind to the viral spike protein can help some patients with severe COVID-19, but mutations in the Omicron variant have made these drugs less effective. The enzyme that Paxlovid targets is less prone to mutation than the spike protein, so Paxlovid retains activity against Omicron and is more likely to be active against new variants. Also, because it acts on a new viral target, it may have additive effects when given with other antiviral drugs.’

Participants recruited to the RECOVERY Trial are randomly allocated to receive one or more trial treatments plus usual standard-of-care, or usual standard-of-care on its own. In the Paxlovid comparison, participants will receive two 150mg nirmatrelvir tablets and one 100mg ritonavir tablet twice daily for five days. The trial aims to recruit at least 4000 patients to each treatment arm, to be compared with at least 4000 patients who receive usual standard-of-care only. The main aim is to assess whether any of these treatments reduce the risk of death among patients admitted to hospital with COVID-19. The trial will also investigate whether the treatment shortens the length of hospital stay or reduces the need for a mechanical ventilator. It is likely to be several months before the first results are available.

Paxlovid is being provided by the UK Department of Health and Social Care. The decision to add Paxlovid to the trial was made by the University of Oxford researchers and the Trial Steering Committee in conjunction with the Chief Medical Officer, following a recommendation by the UK COVID-19 Therapeutics Advisory Panel.

The study is open to all patients hospitalised with severe COVID-19, and is taking place in 177 NHS hospital sites across the UK. Over 47,000 participants have taken part in the RECOVERY Trial so far, making it the largest trial of COVID-19 treatment in the world.

The RECOVERY Trial was launched as an emergency response in March 2020 and has so far discovered four effective treatments for COVID-19: the inexpensive steroid dexamethasone, the arthritis drug tocilizumab, an artificial antibody treatment, now known as Ronapreve, and baricitinib, an anti-inflammatory treatment. These results have been adopted into clinical guidelines worldwide and likely saved many thousands of lives. RECOVERY continues to investigate potential new treatments to counter the threat of new viral variants emerging.

The RECOVERY Trial is continuing to investigate other treatments including empagliflozin, a routine treatment for diabetes, sotrovimab, an investigational monoclonal antibody that targets the Omicron variant, higher doses of the corticosteroid dexamethasone, and the antiviral treatment molnupiravir.