An antibody from a patient who recovered from SARS has been shown to block COVID-19 infection in a laboratory setting, researchers said Monday in another potential breakthrough in the search for coronavirus treatment.

Scientists based in Switzerland and the United States previously isolated the antibodies from the patient in 2003, following the SARS outbreak that killed 774 people.

They experimented with 25 different types of antibodies — which target specific protein spikes on viruses — to see if they could prevent cells becoming infected with COVID-19. Both SARS and the pathogen which causes COVID-19 are coronaviruses, thought to have come from animals, and so their structures are similar.

The researchers identified eight antibodies that could bind to both COVID-19 and the infected cells.

One candidate, known as S309, was shown to have "particularly strong neutralising activity" against COVID-19.

By combining S309 with other less potent antibodies they were able to target different sites on the virus' protein spike, thus reducing its potential to mutate.

The COVID-19 pandemic has seen hundreds of trials for effective treatment launched, including some involving the use of antibodies from recovered patients.

While there were no experiments on humans in the study, published in the journal Nature, its authors said their findings represent "proof-of-concept" that antibodies from SARS can prevent severe COVID-19 infection and spread.

"These results pave the way for using S309- and S309-containing antibody cocktails for prophylaxis in individuals at high risk of exposure or as a post-exposure therapy to limit or treat severe disease," they wrote.