Measles: What You Need to Know?>

Measles: What You Need to Know

by Berkeley Wellness  

Nationwide outbreaks of measles, beginning last October and still on the rise in 2019, have brought this serious disease—previously eliminated in the United States, thanks to the advent of a vaccine in the late 1960s—back into the spotlight.

Twenty-two states have reported cases. Hardest hit has been New York, including Rockland County and parts of Brooklyn in New York City, considered the "epicenter." As of April 29, there were 423 confirmed cases (including two pregnant women) in NYC, where authorities have issued mandatory vaccination orders.

John E. Swartzberg, M.D., an infectious disease specialist at the UC Berkeley School of Public Health and Chair of the Editorial Board of, answers six important questions about measles infection, transmission, and vaccination.

Q. I thought measles was gone in the United States. Why is it back?

A. There are two main reasons. First, though significant progress has been made in reducing global measles incidence, there is still substantial circulation of the virus in other countries. Unvaccinated U.S. residents who travel to countries where measles is widespread or epidemic, and unvaccinated residents of those countries who travel to the United States, are bringing the virus here. Second, a large number of parents in this country are hesitant to have their children vaccinated, and that hesitancy has resulted in an accumulation of unvaccinated populations who can become infected and maintain transmission.

As a result, the virus has infected more than 700 people in 22 states since last October, "the greatest number of cases reported in the U.S. since 1994 and since measles was declared eilminated in 2000," according to the CDC. A series of outbreaks in 2014 sickened 667 people across 27 states.

Q. How contagious is measles?

A. It’s the most contagious of the vaccine-preventable diseases. The average person with measles would be capable of infecting 12 to 18 other people if all his or her contacts were susceptible (either because they were unvaccinated or because they were in the small percentage of people for whom the vaccine isn't effective). That’s far greater than the contagion rate for influenza or chickenpox. And the rate of transmission to susceptible household members is up to 90 percent. That means that if you are infected with measles and live with four unvaccinated people, three of them will likely also get the measles. Like many other viruses, measles is spread mainly through respiratory droplets from coughing, some of which can remain in the air up to two hours, and via surfaces that may be contaminated with those droplets.

Q. If I was vaccinated against the measles decades ago, do I need a booster?

A. If you had only one shot of MMR (measles, mumps, and rubella vaccine), you could consider getting a second one, though it's not essential. A single MMR shot provides about 93 percent protection, meaning 93 percent of people who get it will develop immunity to measles; a second shot ups the protection to about 97 percent. If you don’t have a record of being vaccinated as a child or having had measles, and you were born in 1957 or after, talk with your doctor about how many doses of MMR you might need.

Q. How effective is the vaccine?

A. Very. In the decade before the measles vaccination program began in the late 1960s, an estimated 3 to 4 million people in the United States were infected each year, of whom 400 to 500 died, 48,000 were hospitalized, and another 1,000 developed chronic disability from measles encephalitis (a brain infection). By 2011, in contrast, widespread use of measles vaccine had led to a greater than 99 percent reduction in measles cases in this country. Globally, measles vaccination prevented an estimated 15.6 million deaths between 2000 and 2013 alone.

Q. Can someone be infected with measles without showing symptoms?

A. Yes. It takes about 2 weeks on average for symptoms to appear once a person has been infected. They usually become contagious around the same time that symptoms appear. The main initial symptoms are a cough, runny nose (similar to a head cold), fever, and red, watery eyes. White spots in the mouth (called Koplik’s spots) may develop a couple of days after symptoms start, followed by a skin rash on the third to fifth day.

Q. Are there people who can’t get vaccinated against measles?

A. Yes, some. Severely immunocompromised individuals, including people on immunosuppressive drugs, may have to avoid measles vaccination; they should check with their doctors. Infants can’t get the vaccine until they’re at least 6 months old, and the first dose usually isn’t given until between 12 and 15 months, unless the child will be traveling abroad. So those groups are especially susceptible to measles infection.

Originally published January 28, 2015; updated April 29, 2019.

Also see Life Before Vaccines: My Story.