Federal health officials announced Monday that 764 people have come down with measles this year, more than double the number diagnosed last year.
Though the United States declared measles eliminated in 2000, the disease seems to be making a comeback.
In California, 42 people have been diagnosed with measles this year, with the biggest outbreak in Northern California.
As numbers continue to climb, here are answers to questions about measles, including how to protect yourself against the disease.
I got the vaccine when I was a child. Could I get measles?
Probably not. The measles vaccine is one of the most effective immunizations, protecting 97% of people who come into contact with measles from getting sick. Almost everyone in the U.S. who caught measles this year had not been vaccinated.
The measles vaccine’s half-life — the time it takes for your immunity to fall by half — is 200 years, so people are protected for a lifetime, said University of Maryland public health professor Donald Milton.
“The vaccine is really, really critical,” Milton said.
Is there a booster shot?
Most people don’t need a booster, but there are some exceptions. It depends when you were born.
1989 or after: You most likely got the current version of the vaccine, which is two separate shots and highly effective. You don’t need a booster.
between 1957 and 1988: It’s possible that you got an older single-dose version of the measles vaccine that is less effective. However, officials are not recommending revaccination for this group unless people are traveling internationally or work in healthcare. (There is a smaller group of people who received an alternative version of the vaccine between 1963 and 1967 that was not effective. Officials are recommending re-vaccination for those people.)
before 1957: If you were born before 1957, you are believed to have gotten measles and therefore have natural immunity. Officials are not recommending vaccination for this group unless people are traveling internationally or work in healthcare.
So basically, most people don’t need to be revaccinated unless they work in healthcare or are planning to travel internationally. If you do either of those things, then you should talk to your doctor about measles. A physician can do a blood test to check if you're already immune.
“Most adults are protected against measles — that’s what the science says,” said Dr. Nancy Messoinner, director of the Center for Disease Control and Prevention’s National Center for Immunization and Respiratory Diseases, in a call with reporters. “That includes people who were born before measles vaccine was recommended and even people who only got a single dose of measles.”
That said, there isn’t a downside to getting vaccinated or revaccinated if you’re worried about measles, experts say. So ask your doctor about it.
My baby is too young to get the shot. What can I do?
Typically babies can’t get the measles vaccine until they are 1. But officials are recommending that babies traveling internationally get one dose of the vaccine between 6 months and 11 months. Talk to your child’s pediatrician.
What is measles?
A highly contagious virus, measles typically makes people sick for a few weeks. Before the vaccine was created, every child in America is believed to have gotten measles by age 15.
Measles is spread through coughing and sneezing. It is widely considered one of the most contagious illnesses in the world. Even after a sick person leaves a room, the virus can exist for up to two hours, able to infect an unsuspecting victim.
What happens if I get measles?
Most people who come down with measles feel sick and get a rash, but then they’re fine. Some people, though, are less lucky.
Roughly one in 500 people with measles will die from it, and one in 1,000 will experience brain swelling known as encephalitis. Other serious complications include pneumonia and ear infections that can lead to permanent hearing loss.
In general, children younger than 5 and adults older than 20 are more likely to suffer from serious complications.
“Contrary to what some people think, measles is not a benign childhood disease,” said California health department director Karen Smith in a call with reporters in April.
Why are these outbreaks happening?
American travelers pick up measles from other countries where the disease is spreading widely and then bring it back to the U.S. Californians caught measles this year during trips to the Philippines, India, Ukraine and Thailand, according to the state health department.
The Los Angeles outbreak has been linked to travel to Vietnam and Thailand.
Once measles is introduced into a community, it starts to spread if people there aren’t immune.
A measles outbreak this year in New York City, where more than 420 cases have been confirmed, began when an unvaccinated child returned from a trip to Israel, where there is a major measles outbreak. The illness then began spreading among unvaccinated members of the Orthodox Jewish community.
Measles outbreaks have been increasing in the U.S. and abroad as vaccine coverage falls. For the first time, the World Health Organization in 2019 named vaccine hesitancy one of the world’s greatest health threats.
Why are people being quarantined?
Typically, health officials isolate people once they’re diagnosed with a disease so they don’t spread the infection to others. But L.A. County officials last month ordered hundreds of people quarantined who didn’t have any measles symptoms.
That’s because people who contract measles can be contagious four days before symptoms show up. So officials have to quarantine everyone who isn’t vaccinated but may have been exposed — even if they don’t have symptoms — as a precaution.
It’s the only way to stop an outbreak of a disease that can spread so rapidly from person to person and has such dangerous consequences, said Johns Hopkins infectious disease professor Clare Rock.
“This is really an effort to curb the transmission, because it is so highly, highly infectious and contagious,” Rock said. “It’s really sort of a wise thing to try and ensure that we’re not getting a much wider spread across our population, which is the purpose of the quarantine.”
Is my neighborhood at risk?
People living in areas where measles is already spreading are most at risk. The CDC has a list of places in the U.S. with outbreaks.
In general, California has high vaccination rates, so it’s less likely there will be a giant outbreak in the state. So far, there have been 42 cases, with about 14 of those people were infected after traveling outside the country, according to state officials. The biggest outbreak in California is in Butte County in Northern California.
Communities with low vaccination rates are most susceptible to the spread of measles. Schools keep track of vaccination rates and can be a good indicator of how many people in your neighborhood are vaccinated.
The California counties with the lowest vaccination rates among kindergartners in the 2017-18 school year were largely concentrated in the northern half of the state and include Mendocino, Sutter and Humboldt. The counties in the southern half of California with the lowest vaccination rates are Kern, San Luis Obispo and Imperial.
What happens if I get measles?
If health officials reached out to you because you were exposed to measles, then listen to what they tell you to do.
But if you don’t have any symptoms, don’t do anything! You’re not sick.
The signs of measles are a lot like cold symptoms, including fever and cough. They usually start about two weeks after exposure. But measles patients also get a characteristic red rash that typically begins on the face and spreads downward toward the feet.
If you have a rash, don’t run to the emergency room or urgent care. Call your doctor’s office first so they can make special arrangements for your visit to avoid infecting others.