Scientists say early studies show promising results for a vaccine which could combat a common type of bacteria.
Scientists hope a vaccine could be widely available
Group A streptococcus causes more diseases than any other, ranging from sore throats to the flesh-eating bug necrotising fasciitis.
The researchers from the University of Maryland, Baltimore, US, say their tests show the vaccine is safe for use in humans.
The study is published in the Journal of the American Medical Association.
Group A strep is commonly found on the skin or upper respiratory tract.
Scientists have been working to develop a vaccine which could protect against the bacterium for around 70 years.
This vaccine contains fragments of proteins found on the surface of six types of strep A. It works by priming the body's immune system so it will mount a protective response if it meets these proteins again.
Researchers gave the vaccine to 28 healthy adults aged 18 to 50.
Each person was given three intramuscular injections of either 50 micrograms, 100 micrograms or 200 micrograms of the vaccine.
Dr Karen Kotloff, of the University of Maryland School of Medicine, who led the research, said: "Our findings, albeit in a small number of participants, suggest that in the full dose range tested, the vaccine appears safe and well tolerated."
In an editorial in JAMA, Dr Michael Pichichero, of the University of Rochester Medical Center, New York, said there were still substantial challenges to be overcome in the development of a vaccine.
He said: "There will be a need to conduct large trials involving 10,000 to 60,000 participants to provide assurance that rare adverse events are not associated with vaccination."
Dr Androulla Efstratiou, an expert in the streptococcal bacterium at the Health Protection Agency, told BBC News Online it was a significant study.
Four out of the six strains the vaccine appears effective against are common in the UK.
"It raises very important issues concerning the development, evaluation and potential usefulness of such a vaccine globally."
She said the research provided the first evidence in humans that a vaccine of this type could be effective.
But Dr Efstratiou added: "These are still very early days and there is much to be learned."