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(Reuters) - The United States’ worst measles outbreak in a quarter-century spread to Idaho and Virginia last week as public health authorities on Monday reported 41 new cases of the highly contagious and sometimes deadly disease.

The U.S. has recorded 1,022 cases of the diseases this year as of June 6, in an outbreak blamed on misinformation about vaccines, the U.S. Centers for Disease Control and Prevention said.

The 2019 outbreak, which has reached 28 states, is the worst since 1992, when 2,126 cases were recorded.

Federal health officials attribute this year’s outbreak to U.S. parents who refuse to vaccinate their children. These parents believe, contrary to scientific evidence, that ingredients in the vaccine can cause autism.

“We cannot say this enough: Vaccines are a safe and highly effective public health tool that can prevent this disease and end the current outbreak,” Health and Human Services Secretary Alex Azar said in a statement last week.

Measles 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 that the country risks losing its measles elimination status if the ongoing outbreak, which began in October 2018 in New York, continues until October 2019.