AstraZeneca’s antibody treatment has been shown to be highly effective at preventing Covid-19 in people who may not respond well to vaccines, according to new clinical trial results.

The data showed that patients given a single injection of the antibody treatment, known as AZD7442, were 83% less likely to develop symptomatic cases of the coronavirus than participants who were given a placebo.

An earlier analysis of the trial, conducted three months after the treatment was administered, had shown that the risk of developing severe disease was reduced by 77%.

Six months on from the treatment being administered, no severe cases of Covid-19 or deaths from the virus had been recorded among patients given the antibody cocktail. In a group given the placebo, five participants contracted severe Covid-19 within six months of the trial beginning, and there were two Covid-related deaths.

More than 75% of participants in the trial had underlying conditions that put them at high risk of contracting severe Covid-19, including those whose immune systems were compromised and therefore may have a reduced response to vaccination.

Around 2% of the world’s population is thought to be at risk of not responding well to Covid-19 vaccines, according to AstraZeneca. This includes people receiving dialysis treatment, undergoing chemotherapy and those taking immunosuppressive drugs for conditions like rheumatoid arthritis.

The phase three clinical trial was conducted across 87 sites in five countries: the U.S., the U.K., Spain, Belgium and France. A total of 5,197 people took part, with 3,460 receiving 300 milligrams of AZD7442 and 1,737 being given a saline placebo.

The six-month assessment included data from 4,991 of the participants, with those who chose to leave the trial to get vaccinated being excluded from the data analysis. Subjects will continue to be assessed for 15 months.

‘Compelling results’

In a separate trial, patients with mild-to-moderate Covid-19 who were given one dose of AZD7442 within three days of developing symptoms had their risk of developing severe disease reduced by 88%.

Half of this trial’s 903 participants were given 600 mg of AZD7442, while the other half were given a placebo.

Ninety percent of those included in the second study were considered to be at high risk of developing severe Covid-19 if they contracted the virus.

The trials’ full results have not yet been peer-reviewed, but are set be submitted for publication in a peer-reviewed medical journal.

AstraZeneca said both trials showed that AZD7442 was “generally well tolerated.”

“These compelling results give me confidence that this long-acting antibody combination can provide my vulnerable patients with the long-lasting protection they urgently need to finally return to their everyday lives,” Hugh Montgomery, professor of intensive care medicine at University College London and principal investigator in the trials, said in a press release Thursday.

“Importantly, six months of protection was maintained despite the surge of the delta variant among these high-risk participants who may not respond adequately to vaccination.”

Meanwhile, Mene Pangalos, executive vice president of biopharmaceuticals research and development at AstraZeneca, said AZD7442 was the only long-acting antibody treatment that had phase three data to demonstrate its efficacy in both preventing and treating Covid-19 with one dose.

“We are progressing regulatory filings around the world and look forward to providing an important new option against SARS-CoV-2 as quickly as possible,” he said.

Other companies developing antibody treatments include GSK, Regeneron and Eli Lilly. All three have been granted emergency use authorization by the FDA.

In October, AstraZeneca announced it had asked the FDA for emergency use authorization for AZD7442 as a preventative treatment. It has not yet been granted.

The pharmaceutical giant has agreed to supply the U.S. government with 700,000 doses of its antibody treatment if that request is granted. It also has agreements in place to supply AZD7442 to other countries.