Measles cases spiked 30 percent in 2017, due entirely to poor vaccination rates, the World Health Organization reported Thursday.

More than 6.7 million people, mostly young children, caught measles in 2017, the WHO reported. And 110,000 died from the virus.

That’s way down from the half a million deaths in 2000, but the progress the world made toward eliminating measles through vaccines is being quickly reversed, the WHO said. It’s in part due to economic chaos in countries such as Venezuela or conflict and unrest in countries including Pakistan and Nigeria. But in other countries, such as Italy, anti-vaccine sentiment means more kids are going unvaccinated.

“The resurgence of measles is of serious concern, with extended outbreaks occurring across regions, and particularly in countries that had achieved, or were close to achieving measles elimination,” said Dr. Soumya Swaminathan, deputy director general for programs at WHO. “Without urgent efforts to increase vaccination coverage and identify populations with unacceptable levels of under-, or unimmunized children, we risk losing decades of progress in protecting children and communities against this devastating, but entirely preventable disease.”

Vaccines have prevented 21 million deaths from measles since 2000, WHO said. But global vaccination rates for measles are just 85 percent on average. Only 67 percent of the world population has received the second needed dose of MMR. To stop transmission of the highly contagious virus, 95 percent of a population needs to be vaccinated, WHO said.

Measles is just the first wave of disease that shows up when kids are not vaccinated, said Dr. Peter Hotez, a pediatrician and dean of the National School of Tropical Medicine at the Baylor College of Medicine.

“I call measles a great biomarker of vaccine coverage because it is one of the most highly contagious viruses that we know about,” Hotez told NBC News.

Nine out of 10 people who are not vaccinated against measles will catch it if they are exposed to it – and measles is an airborne virus, so simply walking into a room with someone else who has measles can expose people to the virus.

“If a single person gets measles, 12 to 18 other people get it, typically babies too young to be vaccinated,” Hotez said.

“The first pop-up disease you see is measles because it is so contagious. Measles is the harbinger of things to come.”

WHO is already seeing high rates of measles infections in 2018. In August, WHO reported 41,000 measles cases in Europe alone, making this year the worst year in a decade for measles in Europe.Brazil has nearly 10,000 cases so far this year and Venezuela has more than 6,300.

“The increase in measles cases is deeply concerning, but not surprising,” said Dr. Seth Berkley, CEO of Gavi, the Vaccine Alliance. “Complacency about the disease and the spread of falsehoods about the vaccine in Europe, a collapsing health system in Venezuela and pockets of fragility and low immunization coverage in Africa are combining to bring about a global resurgence of measles after years of progress,” Berkley said in a statement.

“Existing strategies need to change: more effort needs to go into increasing routine immunization coverage and strengthening health systems. Otherwise we will continue chasing one outbreak after another.”

Babies should get a measles, mumps and rubella vaccine as a routine immunization, but the WHO estimated that 21 million infants did not get their shots in 2017. Nigeria, India, Pakistan, Indonesia and Ethiopia had the most unimmunized infants.

Measles can cause a range of symptoms, including fever and a characteristic rash. It can also lead to pneumonia and encephalitis, which can kill. Children who survive severe bouts of measles can become blind or partly paralyzed.

In the U.S., the Centers for Disease Control and Prevention reports 220 cases of measles so far, making 2018 one of the worst years in a decade. “A total of 15 outbreaks (defined as three or more linked cases) have been reported so far in 2018,” the CDC said.

Travelers often bring measles back with them, and in certain spots around the country, low vaccination rates make for good tinder for the virus to take hold and spread.

“This is a self-inflicted wound,” said Hotez, who has written a book about the anti-vaccine movement entitled “Vaccines Did Not Cause Rachel’s Autism.”

“I have been trying to make the point now that the anti-vaccine movement is starting to inflict real public health damage. It’s taken a few years,” Hotez added.

“This should be a wake-up call that the anti-vaccine movement is not a fringe movement. It is a well-organized public health destruction machine.”