A new coronavirus antibody treatment developed by drugs giant AstraZeneca and aimed at people who cannot be vaccinated reduced the risk of developing symptomatic disease by 77%, the company said.

The results of the Provent phase III pre-exposure prophylaxis trial showed there were no cases of severe Covid or Covid-related deaths in those treated with the “antibody cocktail” AZD7442, AstraZeneca said on Friday.

The study of more than 5,000 adults found AZD7442, a combination of two long-acting antibodies, also reduced the risk of developing symptomatic Covid-19 by 77% compared to a placebo.

In the placebo group there were three cases of severe coronavirus which included two deaths, the company added.

The drugs company said the antibody combination, which is delivered through an injection to the muscle, could give people up to 12 months of protection from Covid-19.

It is the first non-vaccine antibody combination modified to provide potentially long-lasting protection that has demonstrated prevention of Covid-19 in a clinical trial, AstraZeneca added.

Sir Mene Pangalos, executive vice-president of biopharmaceuticals R&D at AstraZeneca, said: “We need additional approaches for individuals who are not adequately protected by Covid-19 vaccines.

“We are very encouraged by these efficacy and safety data in high-risk people, showing our long-acting antibody combination has the potential to protect from symptomatic and severe disease, alongside vaccines.

“We look forward to sharing further data from the AZD7442 phase III clinical trial programme later this year.”

More than 75% of participants in the trial had co-morbidities and other characteristics that are associated with an increased risk of severe Covid-19 or cause a reduced immune response to vaccination, AstraZeneca said.

These include those with immunosuppressive disease or taking immunosuppressive medications, diabetes, severe obesity or cardiac disease, chronic obstructive pulmonary disease, chronic kidney and chronic liver disease.

The long-acting antibodies were well tolerated and preliminary analyses showed adverse events were balanced between the placebo and AZD7442 groups, AstraZeneca added.

The participants will continue to be monitored for 15 months, the company said.

AstraZeneca also said that preliminary “in vitro” findings from investigators at Oxford University and Columbia University show AZD7442 neutralises recent emergent Covid strains, including the Delta variant.

Myron J Levin, professor of paediatrics and medicine at the University of Colorado School of Medicine and principal investigator on the trial, said: “The Provent data show that one dose of AZD7442, delivered in a convenient intramuscular form, can quickly and effectively prevent symptomatic Covid-19.

“With these exciting results, AZD7442 could be an important tool in our arsenal to help people who may need more than a vaccine to return to their normal lives.”

AstraZeneca said it will prepare regulatory submissions of the data for health authorities for potential emergency use authorisation or conditional approval of AZD7442.

Professor Penny Ward, visiting professor in pharmaceutical medicine at King’s College London, said the new treatment could be a very important option for patients at high risk from Covid who have responded poorly to vaccination or who must take immune-suppressing treatment for other diseases.

She added: “Indeed it could potentially be game changing for these individuals, who are currently being advised to continue to shield despite being fully vaccinated.

“Despite the success of vaccination some individuals do not respond as well and remain at higher risk of disease, hospitalisation and death. Prophylaxis with passive antibody therapy can help these folks further and reduce morbidity and mortality in this important population subset.

“They can be used to protect people while they undergo cancer treatment, for example.”

But Prof Ward said while the initial data was “encouraging” full publication of the results was need to understand the merits of the product and how to use it “most effectively” in practice.

Helen Rowntree, director for research, services and engagement for Blood Cancer UK, said the Medicines and Healthcare products Regulatory Agency (MHRA) needed to urgently assess the drug for approval for use in the UK.

If approved, the Government needs to draw up plans for giving it to people with blood cancer as quickly as possible, she added.

Ms Rowntree said: “This is great news for people with blood cancer because while their weakened immune systems mean they are less likely to respond to vaccines, this treatment does not rely on the immune system to produce antibodies to fight off the virus.

“This means that this may even be the game changer that potentially gives people with blood cancer the same kind of protection from Covid as the vaccines are already giving people who don’t have blood cancer.”