The researchers, at Imperial College London and King's College London, say their "targeted" approach could lead to a cheaper and more effective vaccine.
In tests, they have injected into a layer of skin on patients they think is a "hotline" to the immune system.
Allergy UK said it was a very exciting development.
Treatment for hay fever is largely through drugs such as antihistamines or steroids. In very severe cases, tablets or injections of pollen under the skin can be given. The doses are gradually increased over three years to boost tolerance to pollen. However, the treatment is expensive.
The research team are trying much shallower injections into a part of the skin packed with white blood cells, part of the immune system. They argue their targeted approach means they can use tiny amounts of pollen - their dose is 2,000 times smaller than current injections - and also need fewer injections.
"It is a totally different route," Dr Stephen Till told the BBC. "The injections are very, very superficial almost flat against the skin."
Improvement The results of early tests on 30 patients, published in Journal of Allergy and Clinical Immunology, suggested the allergic reaction to grass pollen decreased with the vaccine.
A third of the patients were given six injections a fortnight apart. Initially the injection resulted in a large lump on the skin, but over time the size of the lump decreased.
The researchers said this suggested the allergic reaction to grass pollen was being switched off.
They are now starting a clinical trial with 90 patients to see if the vaccine can also reduce other symptoms such as sneezing.
Dr Till said: "If this approach proves to be effective it would define a new scientific and clinical principle that could also be applied to other allergic diseases such as asthma and food allergies.
"This could be a pivotal study in immunological research."
Maureen Jenkins, the director of clinical services at the charity Allergy UK, said this was a "very exciting development" which "offers hope for sufferers".
She added: "The proposed vaccine, if successful, is much quicker and more straightforward than current immunotherapy treatment for hay fever, which takes years. It also has the potential to offer cost savings.
"If this series of injections proves effective in combating hay fever, it will be a wonderful step forward in tackling this common, but often underestimated allergy."
A separate vaccine would have to be developed to help people with allergies to tree pollen.