As dozens of Afghans boarded U.S.-bound planes at the military’s Ramstein Air Base in Germany on Saturday morning, they were the first to do so in three weeks.

Flights of Afghan evacuees waiting at Ramstein resumed this past weekend after a 21-day pause recommended by health officials to prevent the spread of measles, after a handful of cases were detected among arrivals last month.

The base in Germany was the largest reception point for Afghans who had been evacuated in August, and it has welcomed 35,000 people to date.

But while most were not there for more than a week or two, nearly 9,000 remained for a longer period while they received the measles, mumps and rubella (MMR) vaccine and then quarantined according to Centers for Disease Control and Prevention guidelines.

Many also received the Johnson & Johnson COVID-19 vaccine if they were eligible. 

The resumed flights were expected to transport 1,000 Afghan people per day to the United States, though the exact end date of relocation from Ramstein was not announced.

Officials have found 24 total cases of measles among Afghans who had recently arrived in the U.S., most of whom first stay on military bases throughout the country for health checks and while they secure permanent housing. 

As of last week, there were about 53,000 Afghans housed on bases around the United States. And more than 49,000 had received their MMR shot during the new vaccination campaign, which ended Oct. 4.

“It’s been a huge challenge in terms of ensuring that what initially were isolated outbreaks of measles stemming from a pool of unvaccinated people did not grow into a much bigger outbreak,” one senior administration official said of the measles cases late last month. 

“On a crash basis, the U.S. government has undertaken essentially a mass vaccination campaign,” the official added.

Before entering the U.S., Afghans also complete “a rigorous, multi-layered screening and vetting process including biometric and biographic screenings conducted by intelligence, law enforcement, and counterterrorism professionals,” according to a statement from the Department of Homeland Security.