Elizabeth Renstrom—TIME
September 27, 2016 1:29 PM EDT

North, South and Central America are the first region in the world to be declared measles-free, after 22 years of work to banish the highly contagious infection that can result in pneumonia, blindness and death.

For an area to gain a measles-free status, at least three years need to pass without any case of endemic transmission (in other words, the infection did not come in from abroad), and a follow-up has to take place year after year.

Thanks to scientific advances, health experts can find out where exactly the virus has come from when a measles case is reported. For example, it was determined that a significant outbreak of measles linked to a case at Disneyland in California in 2014 had come into the U.S. from another country, and therefore was not an endemic.

The main reasons the Americas are now measles-free is due to a strict vaccination program. “Take the example of the country I come from,” said Bahamas-based Dr. Merceline Dahl-Regis, Chair of the International Expert Committee for Elimination in the Americas. “You have 400,000 people [living there] and six million people who come and visit the country – and we don’t have measles because of high immunization coverage.”

“That’s the simple answer. Poor, male, female, whatever the social class, everyone needs to be immunized; high coverage is how you prevent the reintroduction of measles.”

The Pan American Health Organization (PAHO) will continue to work towards freeing the region of polio and other diseases. Years ago, steps were taken towards declaring the region free of neonatal tetanus (a form of tetanus that occurs in newborns) and, if the PAHO is successful in Haiti, that goal may be reached this year. The PAHO has also made progress in the elimination of Hepatitus B, by vaccinating newborns.

But, as Dr Cuauhtemoc Ruiz-Matus, chief of PAHO/WHO’s Comprehensive Family Immunization Program, made clear, freeing regions of disease is no easy feat. “It’s very hard,” he said. “In some countries, the difficulty was that you had so many migrants… they did not have cars and you couldn’t access them.”

He added that ill-defined borders and conflict in the Americas provided further challenges. “In some of the territories… there’s movement back and forth; that was a particular challenge. Then there were issues relating to countries that are still in conflict – we could not get through to some areas because of the domestic fighting that goes on.”

Various countries in the region invested heavily in interrupting the transmission of the infection. “Ecuador, Colombia, Venezuela and Brazil really deserve a significant mention,” Dr Ruiz-Matus said. “They came through and did an excellent job. And we have all learned so much through these experiences.”

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Write to Kate Samuelson at kate.samuelson@time.com.

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