Measles cases in the U.S. are continuing to jump, and most of the reported illnesses are in children.

Health officials say 465 measles cases have been reported this year, as of last week. That's up from 387 the week before.

The numbers are preliminary. The 2019 tally is already the most since 2014, when 667 were reported. The most before that was 963 cases in 1994.

Cases have been confirmed in 19 states, up from 15 states the week prior. Outbreaks have hit several states, including California, Michigan and New Jersey. New York City accounted for about two-thirds of the U.S. cases reported last week.

Outbreaks have been linked to U.S. communities with pockets of unvaccinated people and travelers who get measles abroad. Around the world measles cases have reached "alarming" numbers, a recent UNICEF report cautioned.

Measles is a viral respiratory illness that is so contagious that if a person is infected, up to 90 percent of the people close to that person who are not immune will also become infected, according to the CDC. The incubation period for measles — the time from when you’re first exposed to when you get sick — is fairly long at 10-12 days and people can be contagious up to four days before symptoms appear.

The Centers for Disease Control and Prevention updated the numbers Monday. Roughly 80 percent of the cases are age 19 or younger. While most of the cases in the U.S. are in children, adults with measles are 10 times more likely to be hospitalized because they’re more likely to get pneumonia — one of the complications.

The CDC recommends that all children get two doses of measles vaccine. It says the vaccine is 97 percent effective.

Contributor Agnes Pawlowski contributed to this report