It started with a traveler from Israel, where measles has been raging for months, making nearly 3,000 people sick and killing at least two people. The person went to New York, where yet another outbreak is under way. And then they visited the Detroit area.

Now, eight people in Oakland County, Michigan, have come down with the insanely contagious and potentially deadly illness—which was once eradicated in the U.S., but is making a comeback thanks to a growing anti-vaccination movement based on debunked conspiracy theories.

Health officials say there is one way to stop the spread in its tracks. “Unvaccinated individuals need to get vaccinated,” Leigh-Ann Stafford, health officer for Oakland County warned.

Since March 13, Michigan health authorities have sent out a series of increasingly worrisome bulletins, each with more confirmed cases and new locations where others may have been exposed to the virus, which can live in the air and infect the unvaccinated for up to two hours.

The list of locations has grown to nearly 30 places, from yeshivas to car washes to big chain stores. Many of them are in the Orthodox Jewish community, where vaccination rates have been lower.

In New York, more than 200 people in two Jewish enclaves have come down with the measles. Health authorities have struggled to contain the outbreak, undermined by a half-dozen yeshivas that have flouted a state order to send unvaccinated students home.

In the Pacific Northwest, nearly 80 cases have been recorded in Washington and Oregon; many of them are in the Slavic community.

There are also scattered cases in a dozen more states, but health officials say a measles diagnosis here and there does not pose the same threat as when a cluster of illnesses is found in communities with higher unvaccinated rates.

In Michigan, health officials noted a special threat: March and April is spring break time, which means people who are infected but not yet showing symptoms could travel and spread measles even further. Babies and children who are too young to be fully vaccinated are at particular risk of contracting the disease.

“All I can say is that as someone who has grandchildren too young to be immunized and a daughter who potentially would be much more dangerously affected by the measles than the general population, I’m horrified that this is even still an issue,” Lisa Shevin of Oak Park told the Jewish News. “I get that some people are concerned about the issue of parental choice, but there comes a time when the good of society as a whole needs to take precedence.”

Because it is so contagious, authorities are asking anyone who suspects they have measles not to just show up to a doctor’s office or emergency room, where one sneeze or cough could sicken others. They should call their health provider and make special arrangements to be seen instead.