The bacterium injects the toxin into cells in the stomach lining, starting a chain reaction which helps it feed.
Vaccines usually involve injecting a harmless version of the bacteria or virus in question, or a large quantity of a protein found within it.
This stimulates the immune system to recognise the bacteria or virus, or its protein, as a foreign intruder, and launch an attack.
However, an Italian team, led by Professor Cesare Montecucco of the University of Padua, believes the toxin is the bacterium's weak point, and a potential target for the body's immune system.
The toxin, called VacA, is injected by H pylori into cells in the stomach lining.
They cause internal structures in the cells to swell up, and spill chemicals called enzymes out.
These help break down stomach mucus, and makes the whole layer of lining cells "leaky", allowing the H pylori bacteria to obtain nutrients from both directions.
Human tests this year
The team hope that their vaccine will begin to be tested in humans later this year.
H pylori is blamed for an estimated 19 out of 20 duodenal ulcers, and the majority of gastric ulcers.
It is also thought to play a part in the development of some stomach cancers - the cancer which causes the fourth highest numbers of deaths in the UK.
It is even suspected of having a role in heart disease.
Some doctors recommend that patients complaining of persistent heartburn and indigestion should be tested for the presence of the bacteria.
If found, they can be eradicated with a combination of drugs.
Other teams, including one based at St James' University Hospital in Leeds, are working to develop a working H pylori vaccine.
The development was reported in New Scientist magazine.