How does measles spread?

Measles is one of the most contagious infectious diseases known. It spreads through the air via tiny respiratory aerosols and droplets released when an infected person coughs, sneezes, or breathes. The virus can survive in the air and on surfaces for up to 2 hours after an infected person has left a room — meaning you can catch measles without direct contact. The basic reproduction number (R₀) is 12–18: each infectious person can infect 12 to 18 unvaccinated contacts in a susceptible population. An infected person is contagious from about 4 days before their rash appears through 4 days after — roughly 8 days total, often before they know they are sick. Measles has no animal reservoir, which means it can only survive by continuously infecting people. This makes herd immunity — achieved through ≥95% two-dose MMR vaccination — the only sustainable way to stop transmission.