The injected therapy, called AZD7442 or evusheld, had previously been shown to confer 77% protection against symptomatic illness after three months, in an earlier readout of the late-stage Provent trial in August.

The Anglo-Swedish company also said a separate study in patients with mild-to-moderate Covid-19 showed a higher dose of AZD7442 cut the risk of symptoms worsening by 88% when given within three days of first symptoms.

The latest results from longer-term follow-ups potentially position AstraZeneca, like rival Pfizer as a future supplier of both Covid-19 vaccines and treatments, with AstraZeneca having said the therapy’s “real advantage” was as a preventative shot.

“These new data add to the growing body of evidence supporting AZD7442’s potential to make a significant difference in the prevention and treatment of Covid-19,” executive vice-president Mene Pangalos said in a statement.