The FTSE 100 group said phase III trials met the primary endpoint, which is the main result the pharma company was seeking, by combining tezepelumab to the standard of care.
The group said it demonstrated a statistically significant and clinically meaningful reduction in the asthma exacerbation rate over the course of a year, compared to the patients on a placebo.
There were no clinically meaningful differences in safety results between the tezepelumab and placebo groups.
The treatment, which is being developed by AstraZeneca in collaboration with US biotech Amgen, was granted Breakthrough Therapy Designation by the US Food and Drug Administration in 2018. It blocks the action of thymic stromal lymphopoietin, a protein that plays a key role across the spectrum of asthma inflammation.
The firm said severe asthma affects 34mln people worldwide, and many patients continue to experience symptoms and frequent episodes despite the use of high-dose asthma controller medicines, biologic therapies and oral corticosteroids.
Shares rose 2% to 8,451.72p on Tuesday morning.