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."
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.