Caused by the measles virus, measles is a highly contagious disease. In general, people who have not been vaccinated or have only received one dose of vaccination, such as new immigrants and domestic helpers, are at high risk of being infected. People who have been infected with measles and become seriously ill can have their respiratory system, digestive system and the brain damaged. In worst cases, it may even cause death. To prevent the outbreak of measles, the most effective method is to vaccinate against the virus.