There is no confirmed outbreak in New Jersey, but the U.S. and North America are seeing high measles activity this year — including hundreds sickened by the highly infectious airborne virus in West Texas — and declining rates of people getting the vaccine, which is 97% effective after two doses.

Schools and daycares are among the most common places for measles exposures, like one that happened in three western North Dakota public schools in early May that led to all unvaccinated students being held at home for 21 days under state law.

Here’s what to know about the measles and how to protect yourself.

What’s happening with measles in the U.S.?

Most U.S. children get vaccinated against measles before entering public school, but increasing numbers of people skipping shots for religious or personal reasons have fueled outbreaks in the U.S. and abroad this year.

Overall, the U.S. has seen more than 1,000 measles cases across 30 states since the beginning of the year, and 11 states with outbreaks — defined as three or more related cases. The largest outbreak in the U.S. has been in Texas, New Mexico and Oklahoma. There are also large outbreaks in Mexico and Canada.

What is measles?

It’s a respiratory disease caused by one of the world’s most contagious viruses. The virus is airborne and spreads easily when an infected person breathes, sneezes or coughs. It most commonly affects kids.

“On average, one infected person may infect about 15 other people,” said Scott Weaver, a center of excellence director for the Global Virus Network, an international coalition. “There’s only a few viruses that even come close to that.”

Measles first infects the respiratory tract, then spreads throughout the body, causing a high fever, runny nose, cough, red, watery eyes and a rash.

The rash generally appears three to five days after the first symptoms, beginning as flat red spots on the face and then spreading downward to the neck, trunk, arms, legs and feet. When the rash appears, the fever may spike over 104 degrees Fahrenheit, according to the CDC.

There’s no specific treatment for measles, so doctors generally try to alleviate symptoms, prevent complications and keep patients comfortable.

People who have had measles once can’t get it again, health officials say.

Can measles be fatal?

It usually doesn’t kill people, but it can.

Common complications include ear infections and diarrhea. But about 1 in 5 unvaccinated Americans who get measles are hospitalized, the CDC said. Pregnant women who haven’t gotten the vaccine may give birth prematurely or have a low-birthweight baby.

Among children with measles, about 1 in every 20 develops pneumonia, the CDC said, and about one in every 1,000 suffers swelling of the brain called encephalitis — which can lead to convulsions, deafness or intellectual disability.

“Children develop the most severe illness,” said Weaver, who works at the University of Texas Medical Branch in Galveston. “The cause of death in these kinds of cases is usually pneumonia and complications from pneumonia.”

How can you prevent measles?

The best way to avoid measles is to get the measles, mumps and rubella (MMR) vaccine. The first shot is recommended for children between 12 and 15 months old and the second between 4 and 6 years old.

“Before a vaccine was developed in the 1960s, everybody got” measles, Weaver said. There is “great data” on the safety and effectiveness of the vaccine, he said, because it’s been around for decades.

“Any of these outbreaks we’re seeing can easily be prevented by increasing the rate of vaccination in the community,” he said. “If we can maintain 95% of people vaccinated, we’re not going to see this happening in the future. And we’ve slipped well below that level in many parts of the country.”

Vaccination rates have declined nationwide since the COVID-19 pandemic, and most states are below the 95% vaccination threshold for kindergartners — the level needed to protect communities against measles outbreaks.

Do you need a booster if you got the MMR vaccine a while ago?

Not usually. People who are vaccinated are considered protected against measles for their lifetime.

Health care providers can test for antibodies and give boosters if needed.

Getting another MMR shot as an adult is harmless if there are concerns about waning immunity, the CDC says. People who have documentation of receiving a live measles vaccine in the 1960s don’t need to be revaccinated, but people who were immunized before 1968 with an ineffective vaccine made from “killed” virus should be revaccinated with at least one dose, the agency said.

People who have documentation that they had measles are immune, and those born before 1957 generally don’t need the shots because so many children got measles back then that they have “presumptive immunity.”

Weaver said people at high risk for infection who got the shots many years ago may want to consider getting a booster if they live in an area with an outbreak. Those may include family members living with someone who has measles or those especially vulnerable to respiratory diseases because of underlying medical conditions.