A clinical trial by Maryland-based vaccine maker Iomai Corporation showed that of 59 people who used the patch -- which slaps on the skin to deliver the vaccine without a needle -- only three found their guts growling with diarrhea.
Comparing this to results from travelers who were given a placebo, the test showed that the patch cut outbreaks of diarrhea by three-quarters.
"These are clinically significant results that suggest that the patch vaccine will address the most significant unmet need for travel medicine: prophylaxis for travelers' diarrhea," said Gregory Glenn, the company's chief scientific officer, in a statement.
"Those who received the Iomai vaccination were much less likely to get sick, and those who were sickened had far milder illness than those who received a placebo."
The findings were presented at the 47th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), billed as the world's biggest meeting on disease-causing microbes, which runs in Chicago until Thursday.
"The results presented at ICAAC are the most robust ever shown in the prevention of travelers' diarrhea," said Herbert DuPont, a doctor from the Center for Infectious Diseases at the University of Texas, who led the trial.
"They suggest we may be near a turning point in the prevention of this common, often serious disease."
The condition, sometimes known as "Delhi belly" for its association with sickly tourists in India, strikes some 20 million travelers a year. The bugs are common in Africa, Asia and Latin America.
Iomai, citing the World Health Organization, said the bacteria kills 380,000 people each year in poor countries.
Its most common cause is the "enterotoxigenic E. coli bacteria," the company said. The patch delivers a toxin caused by the bacteria safely through the skin to trigger an immune response.
The phase two trial headed by DuPont was carried out on 170 volunteers who wore the patches before traveling to Mexico and Guatemala. One further phase of clinical trials is required before the patch can be marketed.
Iomai plans to start these phase three trials in 2008. Its chief executive Stanley Erck, quoted in the statement, valued the potential market for an effective diarrhea treatment at 750 million dollars a year.