This transmission electron microscope image shows SARS-CoV-2 -- also known as 2019-nCoV, the virus that causes COVID-19 -- isolated from a patient in the US. Virus particles are shown emerging from the surface of cells cultured in the lab. The spikes on the outer edge of the virus particles give coronaviruses their name, crown-like. Credit: NIAID-RML

Pharmaceutical giant AstraZeneca on Thursday announced that clinical trials of an antibody-based COVID-19 drug had shown robust efficacy and long-term prevention.

The Anglo-Swedish laboratory follows in the footsteps of US firms Merck and Pfizer, which announced in October and early November respectively that they had developed drugs that could prevent severe forms of the disease, and that could be taken at the first sign of symptoms.

The AstraZeneca AZD7442, made from a combination of two antibodies, has been undergoing final stage to assess its safety and efficacy.

A six-month follow-up trial "showed robust efficacy from a one-time intramuscular (IM) dose of the long-acting antibody (LAAB) combination", it said in a statement.

One 300mg IM dose reduced the risk of developing symptomatic COVID-19 compared to placebo by 83 percent, it added.

More than 75 percent of participants had co-morbidities that put them at high risk for severe COVID-19 if they were to become infected, but no severe cases were recorded.

Another trial to test its efficacy in treating those already suffering from "mild to moderate" COVID symptoms showed that one 600mg IM dose reduced the risk of developing or death by 88 percent.

"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 ," said Hugh Montgomery, professor of intensive care medicine at University College London.

"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."

AstraZeneca said the full results of both would be submitted for publication to a peer-reviewed medical journal.

It has already submitted an application to US regulators for approval of the drug to treat COVID-19.

AstraZeneca's separate COVID vaccine, developed with the University of Oxford, helped enable Britain's speedy COVID vaccination drive after it was approved in December 2020.