Scientists in the UK have just recruited the first participants in the world to be part of a new long-acting antibody study.

If the treatment is effective, it could give those who have already been exposed to SARS-CoV-2 protection from developing COVID-19.

"We know that this antibody combination can neutralise the virus," explains University College London Hospitals (UCLH) virologist Catherine Houlihan.

"So we hope to find that giving this treatment via injection can lead to immediate protection against the development of COVID-19 in people who have been exposed – when it would be too late to offer a vaccine."

This might not be the first antibody treatment for COVID-19 you've heard of. Outgoing US President Donald Trump was given monoclonal antibodies when he came down with the disease, and in the US two different antibody treatments - casirivimab and imdevimab – received emergency approval back in November.

But those antibody treatments are given to patients with mild or moderate COVID-19, who risk progressing to a severe version of the disease.

"In a clinical trial of patients with COVID-19, casirivimab and imdevimab, administered together, were shown to reduce COVID-19-related hospitalisation or emergency room visits in patients at high risk for disease progression within 28 days after treatment when compared to placebo," the FDA explained in a press statement when the drugs were approved.

This new antibody therapy, called AZD7442 and developed by UCLH and AstraZeneca, is a little different.

AZD7442 is a combination of two monoclonal antibodies AZD8895 and AZD1061, which both target the receptor binding domain of the SARS-CoV-2 spike protein.

"By targeting this region of the virus's spike protein, antibodies can block the virus's attachment to human cells, and, therefore, is expected to block infection," the team wrote on the US ClinicalTrials.gov website.

"Amino acid substitutions have been introduced into the antibodies to both extend their half-lives, which should prolong their potential prophylactic benefit, and decrease Fc effector function in order to decrease the potential risk of antibody-dependent enhancement of disease."

Antibodies are little Y-shaped proteins that lock on to a particular section - called an antigen - of a virus, bacterium or other pathogen, and either 'tag' it to be attacked by the immune system, or directly block the pathogen from invading our cells.

Normal antibodies are produced by your body after an infection, while monoclonal antibodies are cloned in a lab and can be injected into a person already infected, to give the immune system a hand in the fight.

The researchers are hoping that AZD7442 – which is just starting the Storm Chaser study (the name for its phase 3 trial) – provides protection for those that have been exposed to the virus but do not yet have symptoms. Effectively, they're trying to stop COVID-19 happening in the first place.

"If you are dealing with outbreaks in settings such as care homes, or if you have got patients who are particularly at risk of getting severe COVID, such as the elderly, then this could well save a lot of lives," University of East Anglia infectious disease expert Paul Hunter told The Guardian.

"If you live with your elderly grandmother and you or someone else in the house gets infected, then you could give her this to protect her."

But they're also hoping it might be effective longer term, over a 6-12 month period, meaning people who can't receive the vaccine for medical reasons have another option to keep themselves safe from the disease.

The researchers are looking at how this could work for people with compromised immune systems in a second trial called PROVENT.

"We will be recruiting people who are older or in long-term care, and who have conditions such as cancer and HIV which may affect the ability of their immune system to respond to a vaccine," UCLH infectious diseases consultant Nicky Longley told The Guardian.

"We want to reassure anyone for whom a vaccine may not work that we can offer an alternative which is just as protective."

We're looking forward to seeing where this leads.