Significant benefits have been seen from a vaccine against dust mite allergy, its manufacturers say.
Dust mites live in soft furnishings
Cytos, a Swiss vaccine company, carried out a small study of their dust mite vaccine.
Patients given the vaccine - which uses DNA - experienced far fewer allergy symptoms such as sneezing, while asthmatics did not have attacks.
UK experts said any research which could help alleviate symptoms was welcome.
Cytos, one of a number of firms developing anti-allergen vaccines, is also hoping to develop ones which are effective against grass pollen, cat hair and tree pollen.
Hay fever is most severe in spring and summer, because of increased pollen levels.
But dust mites, tiny bugs which feed on scales of human skin, are an equally important cause of allergic reactions, because proteins in the excrement of the mites attack the respiratory passages causing the same kind of symptoms as well as asthma.
Existing treatments for hay fever, such as antihistamines and inhaled steroids, suppress symptoms temporarily.
The Cytos vaccine consists of an empty virus filled with DNA designed to trigger a response from the immune system attached to a protein from the dust mite excrement - the allergen - which would usually cause an allergic reaction.
It is designed to boost the activity of the immune system to suppress that allergic reaction.
The suggestion is that other vaccines could be developed using other allergens.
Of 19 patients injected in a Cytos study to check the safety and efficacy of its vaccine, 17 were found to be completely tolerant to the mites, having no allergic reactions.
Two others were found to have improved significantly.
Further data, eight months after the injections were given, showed hay fever symptoms were, on average, slightly worse, but still much better than before the vaccine was given.
Asthma symptoms still appeared to be well-controlled.
Dr Wolfgang Renner, chief executive of the company, said: "Patients experienced a significant and lasting improvement, suggesting that the treatment effectively modified the underlying cause of the disease."
A spokeswoman for Asthma UK said it was pleased the trials were progressing well.
She added: "House dust mite allergen is a common trigger of asthma symptoms in people with allergic asthma so the successful development of a vaccine has the potential to transform many lives.
"We look forward to seeing the results of the next phase of development."