Foreigners planning to attend the Festival of Pacific Arts in Solomon Islands in July are being urged to vaccinate against rubella, also known as German measles.
The health authorities have issued the warning after a first case was recorded on Tuesday and five more a day later.
Officials say due to the airborne nature of the virus, containment is no longer an option.
The Undersecretary for Health Improvement, Dr Cedric Alependava, says a nationwide vaccination program is being organised to start next month.