A COVID-19 antibody cocktail developed by Regeneron and Roche slashed deaths among hospitalised patients whose own immune systems had failed to produce a response, according to the preliminary findings from a large UK study.

"The UK RECOVERY trial found that adding investigational REGEN-COV to usual care reduced the risk of death by 20% in patients who had not mounted a natural antibody response on their own against SARS-CoV-2, compared to usual care on its own," Regeneron said.

Regen-Cov is a combination of two monoclonal antibodies, known as casirivimab and imdevimab, that was designed specifically to block infectivity of SARS-CoV-2, the virus that causes COVID-19.

Regen-Cov can be administered by intravenous infusion (as short as 20 minutes) or by subcutaneous injection (four injections). It is now authorized as a co-formulated single vial, or in individual vials to be administered together.

Recovery is the first trial large enough to definitively determine whether Regen-Cov reduces mortality in patients hospitalized with severe COVID-19.

There were 9,785 patients hospitalised with COVID-19 who were randomly allocated to receive usual care plus the antibody combination therapy or just usual care, of which 30 percent were seronegative.

The drug reduced:

• risk of death
• length of hospital stay
• chances of needing a mechanical ventilator

The trial found that the antibody therapy reduced by a fifth the 28-day mortality of people admitted to hospital with COVID-19 whose immune system had not mounted an antibody response.

This translates into six fewer deaths for every 100 seronegative patients treated with the therapy.

The study which has not been peer-reviewed yet, showed the treatment also shortened the hospital stay of those who were seronegative and reduced their chances of needing a mechanical ventilator.

The Recovery trial marks the first time an antiviral treatment for Covid-19—which targets the virus and not the body has been demonstrated to reduce the risk of death in hospitalized patients.

An inexpensive steroid, dexamethasone, and an anti-inflammatory, tocilizumab, can both reduce mortality in hospitalized patients. But they address the body's response to the virus and not the virus itself, Forbes reported.

Other companies have been developing similar treatments.

Antibody treatments developed by Eli Lilly and Co as well as by Vir Biotechnology Inc with GlaxoSmithKline have received emergency use authorization in the US, Reuters reported.

AstraZeneca recently said its antibody therapy had shown no evidence of protecting people from developing the disease following exposure.

These results could stir more interest in the field for other effective treatments for COVID-19, which are still needed despite the availabilty of several vaccines.

"The trial was conducted at a time when most patients had not been fully vaccinated. These results provide hope to patients who have a poor immune response to either the vaccine or natural infection, as well as those who are exposed to variants for whom their existing antibodies might be sub-optimal." David Weinreich, MD, Executive Vice President, Global Clinical Development at Regeneron, said.

The treatment should be administered on only those who have not already made any antibodies of their own to fight COVID.

It is also really expensive, which costs between between £1,000 and £2,000, BBC reported.

A large, possibly 20 number of people have to be treated with the extremely expensive drug to prevent a single death, Reuters reported quoting Stephen Evans, Professor of Pharmacoepidemiology, London School of Hygiene & Tropical Medicine.

The benefits should not be overstated, professor Evans said, adding that it will be beneficial if patients can be readily identified and treated.

(With inputs from BBC, Reuters and Forbes.)