Measles is considered one of the most contagious viruses known to humans. It has a reproductive number, or R0, of 12-18, which means that if a single individual has measles another 12-18 individuals will also become infected. In most people, measles will cause fever, rash, fatigue, preceded by cough, pink eye (conjunctivitis) and cold symptoms.
Unfortunately, measles is a serious infection (and with a high rate of complications), especially in infants under the age of 12 months not yet old enough to receive their first dose of measles vaccine. According to the Centers for Disease Control and Prevention, about one in four infected individuals will require hospitalization, and one in 20 will experience measles pneumonia, which often requires an admission to the hospital Intensive Care Unit. In some cases, measles can also cause deafness and other neurologic complications.