(Reuters) - The United States recorded 21 new measles cases last week, raising the total number of cases for the year to 1,203 across 30 states in the worst outbreak of the virus since 1992, federal health officials said on Monday.

The U.S. Centers for Disease Control and Prevention said there had been a 1.8% increase in the number of cases of the highly contagious and sometimes deadly disease between Aug. 8 and Aug. 15.

In a sign that the outbreak is slowing, the CDC in recent weeks has reported smaller increases in the number of measles cases, compared with surges of dozens of cases reported per week earlier this year.

Failure to vaccinate poses a public health risk to vulnerable people unable to receive the vaccine, health officials have warned.

The disease was declared eliminated in the United States in 2000, meaning there was no continuous transmission of the disease for a year. Still, cases of the virus occur and spread via travelers coming from countries where measles is common.

CDC officials have warned the country risks losing its measles elimination status if the outbreak, which began in October 2018 in New York state, continues until October 2019.

(Reporting by Gabriella Borter in New York and Manas Mishra in Bengaluru; editing by Patrick Graham and Jonathan Oatis)