The research team at King's College London said the drug was a "game-changer" that could "revolutionise" care.
The findings stem from the realisation that not all asthma or COPD attacks are the same. Instead, different parts of the immune system are over-reacting in different patients. "Now we can see there are different patterns of inflammation, we can be smarter and get the right treatment, to the right patient, at the right time," said Prof Mona Bafadhel, from King's.
Benralizumab is already used in the most severe cases, but the latest research suggests it could be used routinely for around two million attacks in the UK each year. Benralizumab targets a type of white blood cell - called an eosinophil - that can cause inflammation and damage in the lungs.
The study, on 158 people, monitored patients for three months after treatment for a flare-up. They found that people treated with the new therapy were less likely to be admitted to hospital or need another round of treatment. Volunteers also reported improved symptoms and a better quality of life on the new drug.
"This is a game-changer, we’ve not had a change in treatment for 50 years - it will revolutionise how we treat people when they’re really unwell," Prof Bafadhel said.
A larger trial is due to start in 2025 to fully test the findings of this new research, which has been published in The Lancet.