A county in New York state has declared a state of emergency following a severe outbreak of measles.
Rockland County, on the Hudson River north of New York City, has barred unvaccinated children from public spaces after 153 cases were confirmed.
Violating the order will be punishable by a fine of $500 (£378) and up to six months in prison.
Tuesday’s announcement follows other outbreaks of the disease in Washington, California, Texas and Illinois.
Vaccination rates have dropped steadily in the US with many parents objecting for philosophical or religious reasons, or because they believe misleading information that vaccines cause autism in children.
“We will not sit idly by while children in our community are at risk,” Rockland County Executive Ed Day said in a statement.
“This is a public health crisis and it is time to sound the alarm.”
The outbreak in Rockland County is largely concentrated in the ultra-Orthodox Jewish community, the New York Times reported. It is believed it could have spread from other predominantly ultra-Orthodox areas around New York which have already seen outbreaks of measles.
Officials said the order, which bans unvaccinated children from places such as schools, shopping centres, restaurants and places of worship, would last 30 days.
Measles is a highly infectious disease and can cause serious health complications, including damage to the lungs and brain.
But despite the dangers, vaccination rates are declining in many countries.
In the UK, the government is seeking new legislation to force social media companies to remove content promoting false information about vaccines.
There were more than 82,500 cases in Europe in 2018 – the highest number in a decade and three times the total reported in 2017.
The World Health Organization has declared the anti-vaccine movement to be one of the top global health threats for 2019.