The World Health Organization has ranked vaccine hesitancy — the growing resistance to widely available lifesaving vaccines — as one of the top 10 health threats in the world for 2019. That news will not come as a surprise in New York City, where the worst measles outbreak in decades is now underway. Nor in California or Minnesota, where similar outbreaks unfolded in 2014 and 2017, respectively. Nor in Texas, where some 60,000 children remain wholly unvaccinated thanks in part to an aggressive anti-vaccine lobby.

Leading global health threats typically are caused by the plagues and perils of low-income countries — but vaccine hesitancy is as American as can be. According to the Centers for Disease Control and Prevention, the percentage of children who are unvaccinated has quadrupled since 2001, even though the overall utilization of most vaccines remains high. More than 100,000 American infants and toddlers have received no vaccines whatsoever, and millions more have received only some crucial shots.

It’s no mystery how we got here. On the internet, anti-vaccine propaganda has outpace d pro-vaccine public health information. The anti-vaxxers, as they are colloquially known, have hundreds of websites promoting their message, a roster of tech- and media-savvy influencers and an aggressive political arm that includes at least a dozen political action committees. Defense against this onslaught has been meager. The C.D.C., the nation’s leading public health agency, has a website with accurate information, but no loud public voice. The United States Surgeon General’s office has been mum. So has the White House — and not just under the current administration. That leaves just a handful of academics who get bombarded with vitriol, including outright threats, every time they try to counter pseudoscience with fact.

The consequences of this disparity are substantial: a surge in outbreaks of measles, mumps, pertussis and other diseases; an increase in influenza deaths; and dismal rates of HPV vaccination, which doctors say could effectively wipe out cervical cancer if it were better utilized. But infectious disease experts warn that things could get much worse. Trust in vaccines is being so thoroughly eroded, they say, that these prevention tools are in danger of becoming useless. The next major disease outbreak “will not be due to a lack of preventive technologies,” Heidi Larson, a professor at the London School of Hygiene and Tropical Medicine, writes in the journal Nature, but to an “emotional contagion, digitally enabled.”