A measles outbreak that started in the fall of 2018 has many concerned. Here's what you need to know about the virus.

Today, news broke that New York state is fighting its worst measles outbreak since the 1990s, with 122 cases of the highly-contagious virus since September 2018.

“We have been bringing the 1-year-olds back at 13 months to get a second dose,” Dr. Douglas Puder, a pediatrician at Clarkstown Pediatrics in New York's Rockland County, said in a statement. “It’s up to us to keep this from spreading. This could become a truly major epidemic.”

Outside of New York, local news outlets reported over the weekend confirmation of two children with measles–one in Portland, Oregon, and the other in Vancouver, Washington.

According to the Centers for Disease Control and Prevention (CDC), 292 measles cases have been confirmed in 26 states and Washington D.C. as of December 1, 2018.

Right before this past New Year's Eve, Newark Liberty International Airport in Newark, New Jersey, issued a measles alert, informing travelers who were in the airport on the afternoon of December 24, 2018 that they may have been exposed to the disease by one infected individual. In the spring of 2018, Kansas City found itself dealing with two simultaneous measles outbreaks, and in 2015, the measles virus was thrust into the news cycle when the CDC investigated an outbreak of the virus associated with Disneyland Resort Theme Parks. That outbreak saw 51 confirmed cases of measles across the country from December 28, 2014 to January 21, 2015.

The main reason for the current outbreak in New York (Rockland County has seen the bulk of measles cases, with 105 confirmed since the fall of 2018) is that children aren't getting vaccinated for measles when and how they should be, NBC News reports.

Concerned? We asked Drs. Jennifer Lighter Fisher and Stephen Morse to weigh in on some must-know facts about the virus.

1. If you’re vaccinated, you don’t need to worry.
The measles vaccination requires two doses, 28 days apart. While one dose is 85 percent effective, both doses are 98 to 99 percent effective, according to Fisher, a pediatric infectious disease specialist at NYU Langone Medical Center. People who have received both doses—and most have—can consider themselves “protected.”

2. Families with infants should employ “cocoon care.”
The vaccine is not administered until a child is 1 year old, so the best way to protect newborns is to “make sure that family and friends that surround the infant are vaccinated,” or what Fisher calls “cocoon care.”

3. It looks a lot like the flu—at first.
The first symptom of measles is not the spotted rash everyone recognizes. It starts with common symptoms like fever, runny nose or a cough—since the disease is airborne, these symptoms can transmit the virus before you even realize you’ve contracted it. Then, you might notice Koplik spots—salt-like spots inside the cheek. Only after those spots appear will you see the telltale rash on the face and neck.

4. It’s highly contagious.
So contagious, in fact, “you need a 95 percent level of protection in the population to prevent small outbreaks,” says Morse, professor of epidemiology at the Columbia University Medical Center. This is known as “herd immunity.” For comparison, a 50 to 60 percent level of protection could prevent a community from a flu outbreak.

Knowing that, if you believe you or your child has contracted measles, do not rush to the hospital, where patient immunity is likely to be low. “They may be infecting other people and cause a large outbreak,” Morse says. “Call first.”

5. There is no cure.
While the measles is almost entirely preventable by immunization, there is no known treatment or cure after contracting the virus. It typically has to run its course—which takes a minimum of one week, but can often be longer. Morse advises treating the measles like the flu, with ample fluids and bed rest—unfortunately over-the-counter or prescription medications can’t do much to lessen its effects.

But don’t panic: “If it’s uncomplicated, and takes a normal course, most people do recover,” says Morse.