Up to 10,000 Britons with severe asthma could soon benefit from an injected treatment launched today. The small but significant group of patients is thought to be responsible for many of the 69,000 hospital admissions and 1,400 deaths caused by the condition each year.

Trials involving 4,300 patients in different countries including Britain have suggested that adding the treatment to other forms of medication almost halves emergency visits and significantly improves quality of life.

The drug, Xolair, injected every two or four weeks by a doctor or nurse, blocks the action of an antibody that helps trigger allergic asthma. The drug was approved in the US more than two years ago, with Australia, Canada, Brazil and New Zealand following suit, and by European regulators last month. It may cost as much as £7,800 a year but enthusiasts for the drug say treating patients in hospital can cost up to £10,000 a time, with even an average stay costing £4,000.

Stephen Holgate, of Southampton University, a lead investigator in trials, said: "This really is a breakthrough for the treatment of difficult-to-control asthma, where patients can be at significant risk of asthma-related death and regular hospital admission. We finally have a treatment option which can offer effective long-term control, even in very severe disease."

Around 5.2m people are thought to receive treatment for asthma and it costs the NHS about £900m a year, but most people can control their condition through rapidly improving treatments which have cut the death rate from more than 2,000 a year in the mid-1990s. However, as many as 500,000 people may still be unable to manage their condition. The drug will not help anywhere near all of those. It tackles only asthma sparked by allergies to house dust mites, pollen and animal fur, for instance, rather than other types including occupational asthma, or those with a genetic component.

Publicity material suggested the drug could help 50,000 to 100,000, but another British clinician involved suggested between 1,000 and 10,000 teenagers and adults might be nearer the mark at first. Mark Britton, who helped test the drug about four years ago, said it had been "extremely successful" in some patients.

Dr Britton, a consultant physician at St Peter's hospital, Chertsey, Surrey, and chairman of the British Lung Foundation, said: "This is not a cure, but one can surmise this will further reduce death rates."

At a glance

· 1.2 million children and 4.1 million adults in Britain are receiving treatment for asthma

· The condition affects tubes carrying air into and out of the lungs

· It causes breathlessness, wheezing and tightness of the chest

· There are 1,400 deaths a year, about a third in people under 65, and 69,000 hospital admissions

· More than 12.7m working days are lost each year