Measles is highly contagious. That’s because it’s an airborne virus that is transmitted when an infected person breathes, coughs, or sneezes. The infectious droplets come into direct contact with anyone in close contact with the host. The infectious virus can remain in the air for two hours and continue to sicken others long after the person with the virus has left. It can remain on surfaces for up to two hours after initial contact. Nearly 90% of those who come into close contact with an individual with measles will acquire it if not immune. In an unimmunized population, one person with measles can infect 12 to 18 others, which greatly exceeds the infection rate with other viruses like Ebola, HIV, or SARS. With Ebola, for example, one case usually leads to two additional cases, while with HIV and SARS, another four people may become infected.