Children can be protected from the dangerous effects of peanut allergy by slowly building up their tolerance, research by Cambridge University Hospitals has shown.
After six months of the therapy, up to 90% of allergic children taking part in a study could safely eat five peanuts a day.
Lena Barden, 11, from Histon, Cambridgeshire, said she "felt like I had won a prize" after being chosen to take part in the research.
Peanut allergy, which affects one in 50 children, can lead to anaphylactic shock - a potentially fatal immune reaction. It is the most common cause of deaths due to food allergies.
The STOP II trial, the largest of its kind worldwide, involved 99 young people aged seven to 16 consuming carefully measured doses of peanut protein.
Over a period of four to six months, the dose was gradually increased until their bodies could cope with the equivalent of five whole peanuts.
By the end of the study, between 84% and 91% of the participants could safely tolerate 800 milligrams of peanut protein a day - the equivalent of five peanuts.
Study leader Dr Andrew Clark, from Cambridge University Hospitals, said: "This treatment allowed children with all severities of peanut allergy to eat large quantities of peanuts, well above the levels found in contaminated snacks and meals - freeing them and their parents from the fear of a potentially life threatening allergic reaction.
"Before treatment, children and their parents would check every food label and avoiding eating out in restaurants. Now most of the patients in the trial can safely eat at least five whole peanuts. The families involved in this study say that it has changed their lives dramatically."
Although a fifth of the children given oral immunotherapy (OIT) reported allergic reactions, they tended to be mild. The most common symptom was itching around the mouth.
The findings are published in the latest edition of The Lancet medical journal.
Co-author Dr Pamela Ewan, head of the allergy department at Cambridge University Hospitals, said: "We found that OIT is well tolerated and provides protection in most children with peanut allergy in this age group by raising the reaction threshold.
"This large study is the first of its kind in the world to have had such a positive outcome, and is an important advance in peanut allergy research. However, further studies in wider populations are needed."
But she warned: "It is important to note that OIT is not a treatment people should try on their own and should only be done by medical professionals in specialist settings."
Maureen Jenkins, director of clinical services at the charity Allergy UK, said: "The fantastic results of this study exceed expectation. Peanut allergy is a particularly frightening food allergy, causing constant anxiety of a reaction from peanut traces. This is a major step forward in the global quest to manage it."
Lynne Regent, chief executive of the Anaphylaxis Campaign, said: "We welcome the positive results of this important study. Such a good outcome for so many of the children who took part demonstrates the importance of oral desensitisation treatment in transforming the lives of those with food allergy. We look forward to seeing further developments in this area to improve patient outcomes."
Further research and a licensing review will be required before peanut immunotherapy can become generally available to the public, which could take several years.
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