Experts are emphasizing the importance of vaccination against measles after two people in New York and three in New Jersey were diagnosed with the viral illness since the start of the year.

It’s not unusual for sporadic cases of measles to be reported. Last year, 14 people in New York City were diagnosed with the illness, with an additional case elsewhere in New York State.

But an unfolding outbreak of the disease in West Texas and New Mexico has cast a spotlight on measles, which is highly contagious and can prove deadly and is sometimes heralded by a rash. That outbreak has emerged at the same time that Robert F. Kennedy Jr., an anti-vaccine activist who advocates unconventional treatments, has become President Trump’s secretary of health and human services.

With measles so much in the news, residents of New York and New Jersey might be feeling concerned. Here’s what to know about the cases in the region.

Should I be concerned about the local cases?

Neither of the two patients in New York State, both of whom live in New York City, had been vaccinated against measles — one was an infant and too young to be immunized — and the cases are not related, according to the city’s health department. The first case was reported in January, and the second in February. Both patients have recovered.

In New Jersey, all three people with confirmed cases of measles this year were not vaccinated against the virus. A person from Bergen County who had traveled internationally was the first of the three patients to be diagnosed, on Feb. 14, according to the state’s health department. Two people who had been in close contact with the first patient were diagnosed nearly a week later and were quarantined to minimize the chances of spreading the virus.

One of the New Jersey patients was hospitalized, but all three have recovered, according to the health department.

New York and New Jersey have issued advisories urging residents to be alert for symptoms and to check their vaccination status. Symptoms can include a rash, fever, cough and eye inflammation, and the virus can sometimes cause pneumonia or brain swelling, both of which can be deadly.

New Jersey officials warned that people who visited the emergency department at the Englewood Hospital between 11:30 a.m. and 5:30 p.m. on Feb. 9 might have been exposed, and urged them to contact their doctor if they experienced symptoms.

Vaccines are the best protection.

Vaccines are the best way to avoid becoming sick with measles, according to experts. The measles vaccine also protects against mumps and rubella, and is typically administered to children in two doses: one when they are between 12 and 15 months old, and another when they are 4 to 6 years old.

The measles, mumps and rubella vaccine, often called the M.M.R. vaccine, is “one of our best,” said Dr. Roy Gulick, chief of the infectious diseases division at Weill Cornell Medicine and NewYork-Presbyterian. People who have received both doses are 97 percent immune to the virus.

In a statement, Dr. Michelle Morse, the acting commissioner of New York City’s health department, urged New Yorkers to make sure they and their children were vaccinated.

“Vaccination not only protects the person who gets vaccinated, but also contributes to community protection by helping stop the spread of the disease and keeping infants and others who can’t be vaccinated safe,” Dr. Morse said.

Vaccination rates in the region are high, but lower for toddlers.

In New York and Connecticut, 97.7 percent of kindergarten students had received the standard set of required childhood vaccinations, including the M.M.R. vaccine, last school year, one of the highest rates in the country, according to the U.S. Centers for Disease Control and Prevention. Far fewer younger children in New York had received a first dose of the M.M.R. vaccine as of Jan. 1. About 81 percent of 2-year-olds had been immunized, according to the state health department — well below the 95 percent experts say is needed to effectively prevent the virus from spreading.

Vaccination rates among New Jersey kindergartners were short of the 95 percent threshold in 2023, at about 93 percent. That’s a slight decline from the year before, as more families in the state have claimed religious exemptions to vaccine requirements for students.

Nationwide, the rate of kindergartners vaccinated dropped from 95 percent to 93 percent between 2019 and 2022, according to the C.D.C. In 2023, the rate dipped even lower.

After a 2019 outbreak, case counts have been mostly low in New York.

Small outbreaks of measles crop up periodically across the United States. New York City reported 14 cases last year, but in 2023 there was just one reported case. In the three-year period before that, no cases were recorded in the city. New Jersey had seven cases last year and one the year before.

In 2019, an outbreak in New York City resulted in more than 600 cases after travelers from Europe and Israel, where vaccines are less common, brought the virus to the city. The outbreak, which affected other states including California and Michigan, was the worst in the United States in decades. City officials responded by declaring a public health emergency and mandating vaccines in some Brooklyn neighborhoods.

Most outbreaks in the past two decades have been fueled by travel between the United States and a country where the virus remains common.

Before vaccines, measles infected between 3 million and 4 million people each year, killing 400 to 500, according to the C.D.C. After the first vaccine was licensed and released in 1963, infection rates declined, and in 2000, the virus was no longer being continuously transmitted in the United States.