The number of measles cases reported in the U.S. this year has reached 1,001, the Centers for Disease Control and Prevention reported on Wednesday.
Health and Human Services Secretary Alex Azar said his agency has been "promoting the safety and effectiveness of vaccines, amid concerning signs that there are pockets of undervaccination around the country."
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"The 1,000th case of a preventable disease like measles is a troubling reminder of how important that work is to the public health of the nation," he said in a statement.
"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," he said, adding that the measles vaccine is given safely to millions of children and adults every year.
Last week, the CDC reported that measles cases had reached their highest level in 27 years, causing concern among public health officials that the country could soon lose its measles elimination status.
"Measles is an incredibly contagious and dangerous disease," Azar said. "I encourage all Americans to talk to your doctor about what vaccines are recommended to protect you, your family, and your community from measles and other vaccine-preventable diseases."
The majority of cases have occurred in New York City and Rockland County, New York. There was also a smaller outbreak, with 40 confirmed cases, in Oakland County, Michigan. That outbreak was declared over on Wednesday.
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