New York Gov. Andrew Cuomo (D) on Thursday evening signed a measure banning religious exemptions for vaccinations into law, as the state wrestles with a measles outbreak that has affected more than 1,000 people this year alone.

“The science is crystal clear: Vaccines are safe, effective and the best way to keep our children safe,” Cuomo said in a statement. “While I understand and respect freedom of religion, our first job is to protect the public health and by signing this measure into law, we will help prevent further transmissions and stop this outbreak right in its tracks.”

Under the law, that state allows for a 30-day time period for unvaccinated students to demonstrate that they’ve started obtaining the required vaccines.

New York has been grappling with its largest measles outbreak in years, thanks in large part to the spread of junk science by anti-vaccine groups, which falsely claim that vaccines cause autism in children, a claim that has been disproven time and time again. The groups have been particularly successful in spreading misinformation to religious communities, like New York’s ultra-Orthodox Jewish community in Brooklyn.

The state’s ongoing anti-immunization crisis appears to be part of a broader national trend, as outbreaks crop up in states across the country. In fact, residents from New York have infected people in four other states. More than half the states in the country have reported cases of measles to the Centers for Disease Control and Prevention (CDC), including Arizona, California, Colorado, Connecticut, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kentucky, Maine, Maryland, Massachusetts, Michigan, Missouri, New Mexico, Nevada, New Hampshire, New Jersey, New York, Oklahoma, Oregon, Pennsylvania, Texas, Tennessee, Virginia, and Washington.

All 50 states have laws requiring vaccines for students, but few ban all non-medical exemptions to vaccines, despite the current widespread crisis. According to the National Conference of State Legislatures, only four states — California, Mississippi, West Virginia, and Maine — have banned both religious and personal belief exemptions to immunizations.

While several states — including Oregon, Colorado, and Connecticut — are currently considering legislation to eliminate some non-medical exemptions, outbreaks of a once-rare disease continue to plague the country. In the 1960s, measles were largely eradicated thanks to the introduction of the vaccine.

And the problem is not just measles. The anti-vaccination movement has triggered a disturbing resurgence of other preventable illnesses, like chickenpox. In addition, the 2017-2018 flu season saw the lowest vaccination rate and the most deaths in decades, with nearly 80,000 reported deaths, including more than 180 children. According to the CDC, 80% of those children had not received the flu vaccine.