Paxlovid UK: how new oral Covid antiviral treatment works, effectiveness, and who can take it

A new oral Covid-19 antiviral treatment has been given approval for use in the UK, the government has announced.

The treatment, called Paxlovid, has been approved by the Medicines and Healthcare products Regulatory Agency (MHRA) after the regulator found the drug to be safe and effective at reducing the risk of hospitalisation and death in people with mild to moderate coronavirus infection, who are at an increased risk of developing severe disease.

How does it work?

The drug, developed by Pfizer, is an antiviral medicine with a combination of active ingredients, PF-07321332 and ritonavir, that works by inhibiting a protease required for virus replication.

This prevents it from multiplying, keeping virus levels low and helping the body to overcome the viral infection.

Ritonavir slows the breakdown of the second ingredient PF-07321332 in the body, thereby increasing its effectiveness.

The two active substances of Paxlovid come as separate tablets that are packaged together and taken together orally twice a day for five days.

PF-07321332 is a new antiviral and has not been approved for use before, whereas ritonavir has been used alongside some HIV medicines for many years to ‘boost’ their activity, which is similar to what it is doing for PF-07321332.

How effective is it?

In a clinical trial of high-risk adults with symptomatic Covid-19 infection, a five day treatment course of Paxlovid reduced the risk of coronavirus related hospitalisation and death within 28 days by 89%, when compared to a placebo group when treatment was started within three days of the onset of symptoms.

The number of hospitalisations and deaths were 0.8% (three out of 389) in the Paxlovid group compared with 7% (27 out of 385) in the placebo group.

Similarly positive results were also seen in patients when treatment was started within five days of the start of symptoms.

Based on the clinical trial data, Paxlovid is most effective when taken during the early stages of Covid-19 infection.

As such, the MHRA recommends its use as soon as possible and within five days of the start of symptoms.

Who can take it?

The drug has been authorised for use in people aged 18 and above who have mild to moderate Covid-19 infection and at least one risk factor for developing severe illness.

These risk factors could include obesity, older age (people aged 60 years and over), diabetes mellitus and heart disease.

It is still too early to know whether the Omicron variant has any impact on Paxlovid’s effectiveness, but the MHRA said it is proactively working with the company to establish this.

Dr June Raine, MHRA chief executive said: “Today we have given our regulatory approval for Paxlovid, a Covid-19 treatment found to cut Covi-19 related hospitalisations and deaths by 89% when taken within three days of the start of symptoms.

“We now have a further antiviral medicine for the treatment of Covid-19 that can be taken by mouth rather than administered intravenously.

“This means it can be administered outside a hospital setting, before Covid-19 has progressed to a severe stage.

“I hope the announcement today gives reassurance to those particularly vulnerable to Covid-19, for whom this treatment has been approved. For these individuals, this treatment could be life-saving.”

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