Patients blighted by hay fever could markedly reduce symptoms after a three–year course of treatment, but not after two years of treatment.“Hay fever causes major impairment of sleep, work and school performance and leisure activities during what for most of us is the best time of the year,” said Professor Durham.

Describing the current findings, Professor Durham said: “This study shows that whereas both immunotherapy treatments were highly effective, two years of treatment was insufficient for long–term benefits.

“Clinicians and patients should continue to follow international guidelines that recommend a minimum of three years’ treatment.”

Previous studies published by Imperial researchers have shown the long–lasting benefits of both immunotherapy injections and pills for severe hay fever – benefits which persist for at least two to three years after the treatment has stopped.

Professor Durham added: “We have reconfirmed that both treatments are effective but that in order to get the long–term clinical benefits after stopping the treatment, you have to take it for three years.”

Researchers at Imperial have a long legacy with immunotherapy dating back to 1911, when a grass pollen injection treatment was first shown to be highly effective in treating hay fever.

Previous research has shown that a type of immunotherapy that exposes patients to increasing amounts of grass pollen over time is an effective way to reduce severe symptoms in the long term.

But in a new study, published in the journal JAMA, scientists from Imperial College London have found that a two–year course of treatment is not enough to achieve lasting effects, bolstering previous findings that more time is needed taking the medication to get lasting benefit.

“You treat patients for three years and then they have a big improvement in their hay fever for several years afterwards,” said Professor Stephen Durham, Head of Allergy and Clinical Immunology at the National Heart and Lung Institute at Imperial and clinical lead for allergy services at Royal Brompton Hospital, who led the study.

“Exposing people to grass pollen in this way is a very effective treatment for people who really have debilitating hay fever.”

The latest study involved patient volunteers at Royal Brompton Hospital in London, which runs a world–class allergy clinic, researchers tested the effectiveness of two immunotherapies prescribed by the NHS which use grass pollen extract: an injection and a pill taken under the tongue.

It was the first head to head trial of the two therapies, in which researchers set out to see if a two–year treatment could achieve the same long–lasting benefits to patients as seen with three–years of immunotherapy, potentially leading to clinical cost savings.

The study was a double blind, placebo–controlled trial in which 106 patients were randomised to one of three treatment groups: injection, tablets and placebo.

Patients had moderate to severe hay fever and were administered either the daily oral treatment, weekly injections for 15 weeks followed by monthly boosters, or a placebo. A total of 92 patients completed the study. After a two year course of treatment, the results showed that both therapies were effective at tackling symptoms, with patients reporting a dramatic improvement in their quality of life. However, one year after patients had stopped taking the medication the effects were no better than the placebo group.

Describing the current findings, Professor Durham said: “This study shows that whereas both immunotherapy treatments were highly effective, two years of treatment was insufficient for long–term benefits.

“Clinicians and patients should continue to follow international guidelines that recommend a minimum of three years’ treatment.”