A four-monthly jab may one day replace the need to regularly take pills to control blood pressure, scientists say.
High blood pressure is a risk factor for heart disease
A team from the Swiss biotechnology firm Cytos found the vaccine against a hormone in the blood significantly cut blood pressure, the Lancet reported.
The jab was tested on 72 patients with high blood pressure and it was found to work without serious side-effects.
The researchers and independent experts said the findings were promising but large-scale trials were now needed.
High blood pressure, which affects a quarter of all adults, doubles the risk of dying from heart disease or stroke and is blamed for 60,000 deaths a year in UK.
Those who are being treated for it often have to take a daily course of pills to keep it under control.
But many people do not keep to their treatment regimes as people with high blood pressure do not display symptoms.
The researchers believe the vaccine, which works against the hormone angiotensin, which causes blood vessels to constrict and increase blood pressure, may offer a simple alternative.
They tested two different doses of the vaccine - 300 microgrammes and 100 microgrammes - as well as a dummy vaccine during the 14-week trial.
The jabs were given at the start, and after four weeks and 12 weeks - enough to give a patient four-month resistance.
Neither dose significantly lowered blood pressure at night.
But during the day the larger dose significantly lowered blood pressure, especially during the late morning peak when blood pressure is known to increase.
And, importantly, the vaccine did not have any serious side-effects with the worst being mild flu-like symptoms.
Lead researcher Dr Martin Bachmann said the vaccine could offer a much more simple way of controlling blood pressure and could be administered during regular visits to the doctor.
"Such a regimen is likely to promote adherence to treatment, but will need to be supported by clinical data."
Professor Jeremy Pearson, of the British Heart Foundation, agreed more research was needed, but described the results as promising.
"Immunisation may be of particular benefit to people who find it difficult to stick to high blood pressure medication, but there is still a long way to go before this approach replaces the highly-effective current treatments.
"Looking after your heart through regular exercise, cutting down on salt, and only drinking in moderation remain the best ways in which we can prevent high blood pressure."
Professor Graham MacGregor, chairman of the Blood Pressure Association, added: "This study demonstrates an interesting new way to lower blood pressure."
Other firms are also known to be testing blood pressure vaccines.