Anti-vaxxers are among the top 10 health threats facing the world in 2019, the World Health Organization says.

The movement against vaccinations has taken hold in a number of countries, including the United States. The percentage of American children aged 19 to 35 months who have not been vaccinated has quadrupled since 2001, according to U.S. Centers for Disease Control and Prevention data, Newsweek reported.

A growing number of people in many U.S. states are anti-vaccination, according to a recent study in the journal PLoS One.

"Since 2009, the number of 'philosophical-belief' vaccine non-medical exemptions has risen in 12 of the 18 states that currently allow this policy: Arkansas, Arizona, Idaho, Maine, Minnesota, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Texas and Utah," the study authors wrote, Newsweek reported.

The other top 10 global health threats include: air pollution and climate change; non-communicable diseases such as cancer, heart disease and diabetes; global flu pandemic; antimicrobial resistance; Ebola and other highly dangerous pathogens; weak primary health care; dengue; HIV; and lack of access to basic health care.