A large study of Pfizer’s experimental antiviral pill, paxlovid, has found that the drug can cut hospitalisations and deaths from Covid by nearly 90%, the company has said.
The US firm’s encouraging results, which are described in a press release but not yet peer-reviewed, suggest oral pills that can be taken at home are poised to take an increasing burden off hospitals that are still overstretched with Covid patients.
The company released the study data on Friday, a day after the UK medicines regulator announced it had approved molnupiravir (Lagevrio), a drug developed by Ridgeback Biotherapeutics and Merck Sharp and Dohme, as the first oral antiviral pill for Covid.
Under deals announced in October, the UK expects to receive 480,000 doses of molnupiravir this year, with 250,000 courses of paxlovid due in late January. Paxlovid is a combination of an antiviral drug with ritonavir, a drug usually used to treat HIV/Aids.
The latest data on paxlovid come from an interim analysis of 775 adults enrolled on the study. Those taking the drug had an 89% reduction in their combined rate of hospitalisation or death after a month, compared with patients taking a placebo. Fewer than 1% of patients taking the drug needed to be admitted to hospital and none died. In the comparison group, 7% were admitted to hospital and there were seven deaths.
Dr Mikael Dolsten, Pfizer’s chief scientific officer, said: “We were hoping that we had something extraordinary, but it’s rare that you see great drugs come through with almost 90% efficacy and 100% protection for death.”
Those who took part in the study were unvaccinated, had mild to moderate Covid, and were considered at high risk of hospitalisation because of underlying conditions such as obesity, diabetes or heart disease. The treatment began within three to five days of patients displaying symptoms and lasted for five days.
The benefits of the drug led to the trial being stopped early on the recommendation of an independent group of medical specialists.
As with molnupiravir, which was found to halve hospitalisations and deaths in at-risk patients, paxlovid treatment must be started soon after symptoms appear so that the drug can prevent coronavirus from replicating and spreading in the respiratory system to cause severe disease.
According to Pfizer, a review of safety data in 1881 patients found side-effects in 19% of those who took paxlovid and in 21% of those who received the placebo.
Although supplies of the pill are due in the UK early next year, the treatment has yet to be approved by medicines regulators.
Dr Siu Ping Lam, the director of licensing at the Medicines and Healthcare products Regulatory Agency (MHRA), said: “We look forward to receiving an application from Pfizer for their antiviral [paxlovid]. As with any medicine, it would only be approved if the expected standards of quality, safety and effectiveness have been met.”
Molnupiravir works by interfering with the coronavirus’s genetic code, a novel approach to disrupting the virus, while Pfizer’s drug belongs to a much older family of antiviral drugs known as protease inhibitors, which revolutionised the treatment of HIV and hepatitis C. Protease inhibitors block a key enzyme that viruses need to multiply in the body.
Prof Jonathan Ball, a molecular virologist at the University of Nottingham, said it had taken longer to develop antivirals than vaccines for Covid because the process was more difficult. “The vaccine platforms had been trialled in humans and so, with a few important tweaks – training them to target the new coronavirus – they were pretty much ready to go into human trials,” he said.
“With antivirals, the process is more laborious. You have to show that the drug inhibits the virus in the lab, and in the case of a totally new drug – show that it’s safe. First in animals then humans. This all takes time,’ he added. “Even the antivirals that are appearing now have been developed for other viruses, so a lot of the preliminary work had already taken place.
“We must remember this was a virus discovered less than two years ago, so the progress in preventing and treating the infection has been phenomenal.”