An antibody injection developed by AstraZeneca provides robust protection against severe COVID-19, potentially providing a prophylactic for people who fail to respond to vaccination, new data show.

The company has announced that the long-acting therapy, dubbed AZD7442, could be used for the prevention or for treatment of mild disease and could be particularly useful for severely immunocompromised patients.

The therapy is derived from antibody immune B-cells from those who have recovered from SARS-CoV-2 infection.

Results from two phase III trials — dubbed PROVENT and TACKLE — which are yet to be published in a peer-reviewed journal, suggest the therapy protects against severe disease and death for at least six-to-nine months following administration.

“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 everyday lives,” said principal investigator Professor Hugh Montgomery, from University College London in the UK.

In the PROVENT pre-exposure prophylaxis trial, the researchers assessed the efficacy and safety of a single 300mg intramuscular injection of AZD7442 in some 5200 unvaccinated adults, three-quarters of whom had comorbidities that put them at high risk of disease.

Compared with placebo, the therapy reduced the risk of developing symptomatic COVID-19 by 83% over a median six months’ follow-up

The TACKLE study investigated a 600mg dose of the biologic as a treatment in 900 high-risk patients with mild-to-moderate COVID-19 disease.

The investigators found that AZD7442 slashed the risk of severe COVID-19 or death from any cause by 88% versus placebo.

In both trials, the treatment was well tolerated and with no new safety issues identified.

Participants will be followed for 15 months, but the primary analyses suggest that protection against COVID-19 lasts for at least six or nine months in the PROVENT and TACKLE trials, respectively.

Melbourne immunologist Associate Professor Mark Hew said that although questions remained, the news signalled the advent of more advanced therapies for COVID-19.