Measles starts with a cough, fever, runny nose, and watery eyes, surfacing seven to 14 days after infection. Three to five days after symptoms begin, the red measles rash appears, starting on the face and spreading down the body.
In the worst cases, the disease can lead to serious complications such as deafness, pneumonia, swelling of the brain, and death. Children younger than age 5, people with weakened immune systems, and pregnant women are especially at risk for a severe case.
“Measles can lead to a lower immune system and a heightened risk of infection from other viruses and bacteria,” Dr. Roberts says. “It is also a cause of keratitis (inflammation of the cornea), which can lead to blindness.”
If you survive measles, you are also at higher risk for sclerosing panencephalitis (SSPE), an incurable degenerative brain and nervous system disorder that causes symptoms such as depression, uncontrolled movements, and dementia.
Measles is highly contagious—it’s easier to catch than the flu or COVID-19. The basic reproductive number (known as the R0, pronounced “R naught”)—a metric used to describe the contagiousness of an infectious agent—is between 12 and 18 for measles, Dr. Roberts explains. That means a person with measles is likely to infect 12 to 18 people who have no immunity, he says.
The virus can be spread to others anytime from four days before to four days after the measles rash appears. It can happen after someone with the measles has coughed or sneezed, when other people breathe the contaminated air or touch an infected surface, then touch their eyes, nose, or mouth. The virus can linger on a surface or in the air for two hours.
Measles tends to spread when people who live in an area where an outbreak is occurring travel to a location that has low measles vaccination rates—places where people are vulnerable, Dr. Roberts says.
However, “communities with a high percentage of vaccinated people have herd immunity, and measles will have a hard time growing to the size of an outbreak in those places,” he says. (Herd immunity is achieved when a large majority of a population is immune to a specific disease, due to vaccination or previous infection.)
“The measles vaccine is a tremendous success story and speaks to the power of vaccination in eliminating such a contagious disease,” Dr. Roberts says.