People at a heightened risk of Covid-19 were given fresh hope on Saturday when an experimental alternative to a vaccine began late-stage trials in UK city of Manchester.
The drug, developed by industry heavyweight AstraZeneca, could be used to protect those with a weakened immune system.
The treatment differs from a vaccine because it introduces antibodies, rather than prompting the body's immune system to make them.
The phase three trial will be tested on 5,000 people across the US and Europe, with 1,000 being recruited in Manchester and the UK.
"What we are investigating in this study is whether we can provide protection by giving antibodies that have been shown to neutralise the virus, by injection into the muscle," said Professor Andrew Ustianowski, chief investigator on the UK study.
"The hope is that this will then provide good protection for many months against infection."
The cocktail combines two monoclonal antibodies and could also be used to treat and prevent progression of Covid-19 in those already infected.
Monoclonal antibodies mimic natural antibodies that the body generates to fight off infection. They can be synthesised in the laboratory and are already used to treat some types of cancer.