An experimental drug developed by AstraZeneca reduces the risk for serious illness or death from Covid-19, company officials announced Monday.

The drug, a combination of two monoclonal antibodies called AZD7442, lowers the risk of severe Covid-19 or death by 50 percent in people who have had symptoms for seven days or less, data from a clinical trial showed.

Monoclonal antibodies are lab-created proteins modeled on those produced by the immune system to fight off infections.

AZD7442 is delivered via injection and both prevents serious illness and treats its symptoms, the company said.

It is designed to protect people who do not develop a sufficient immune response to Covid-19 vaccines, it said.

“[Our] positive results show that a convenient intramuscular dose of AZD7442 could play an important role in helping combat this devastating pandemic,” Hugh Montgomery, the trial’s principal investigator, said in a press release.

“AZD7442 … can be used to protect vulnerable populations from getting Covid-19 and can also help prevent progression to severe disease,” he said.

Monoclonal antibodies manufactured by Regeneron, Lilly and GlaxoSmithKline, have already received emergency use authorizations from the Food and Drug Administration to treat mild-to-moderate Covid-19.

Regeneron’s drug appears to protect against symptomatic illness, while these others have reduced the risk for hospitalisation or lowered the amount of virus in the systems of those infected, according to other studies.

AstraZeneca, which also makes a Covid-19 vaccine, has asked the agency for similar approval for AZD7442 as a preventative therapy, company officials said Monday.

In this clinical trial, conducted in 13 countries with more than 900 adult participants, half of those enrolled were treated with AZD7442 while the remainder were given a placebo, or treatment that provides no clinical benefit, according to the company.

The trial results have not yet been published in a medical journal and, thus, have not been peer-reviewed, it acknowledged.

“An early intervention with our antibody can give a significant reduction in progression to severe disease, with continued protection for more than six months,” Mene Pangalos, AstraZeneca executive vice president, said in a press release.