The measles outbreak that led to a state of emergency in New York’s Rockland County began far away: in an annual Hasidic pilgrimage from Israel to Ukraine.

It is emblematic of a series of fierce, sometimes connected measles outbreaks — in places as diverse as Indonesia, the Philippines, Madagascar and Venezuela — that have shaken global health officials, revealing persistent shortcomings in the world’s vaccination efforts and threatening to tarnish what had been a signature public health achievement .

In 2001, the United Nations declared war on measles. With help from the federal government, the American Red Cross and big donors like Ted Turner and Bill and Melinda Gates, the U.N. began the Measles and Rubella Initiative and created Gavi, the Vaccine Alliance.

Together, they poured billions of dollars into buying vaccines and helping countries deliver it safely, which meant building refrigerated storage facilities, supplying clean needles, training vaccinators and countering other logistical obstacles common in poor countries.