The United States reached its highest number of measles cases in over 33 years on Monday, hitting 1,277 confirmed cases across 38 states and Washington, D.C.

The country reached the highest number of cases of the vaccine-preventable disease since 1992, when health officials recorded more than 2,100 cases. Measles cases have been on the rise following an outbreak in West Texas earlier this year.

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At least 155 people have been hospitalized, and three people have died from measles this year. Around 92% of measles cases this year were in people who were either unvaccinated or whose vaccination status was unknown, according to the Centers for Disease Control and Prevention.

Texas remains the hardest-hit state with more than 700 reported cases.

Measles was declared eliminated in 2000 in the U.S., but cases have increased in recent months amid rising anti-vaccine sentiment.

Public health experts have said the U.S. is slated to lose its disease elimination status if there is a continuous spread of linked measles cases for more than 12 months.

Just under 93% of people in the U.S. are vaccinated against measles. According to the CDC, a 95% vaccination threshold must be reached to achieve herd immunity. Measles is a highly contagious virus, with up to 90% of unvaccinated people contracting it if exposed.

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The disease is most dangerous to children under the age of 5. Symptoms include fever, cough, runny nose, and white spots on the skin called Koplik spots. In every 1,000 children who contract measles, one to two are projected to die.

There is no specific cure or treatment for measles, according to the Mayo Clinic.