There’s a “reasonable chance” that the US will soon lose its status as a country that has eliminated measles. That’s according to Dr. Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention.

The World Health Organization considers a disease eliminated from a country or region if it has gone at least 12 months without continuous spread of said disease. (This is different from disease eradication, which is when a disease is completely stamped out globally. Humans have only managed to eradicate two diseases: smallpox and rinderpest, which infects cattle and other ruminants.)

The US triumphantly declared measles eliminated in 2000—after spending decades tenaciously working to promote widespread vaccination. (The CDC had originally hoped to have it eliminated by 1982.) And in 2016, the WHO declared measles eliminated from the Americas altogether. WHO’s Regional Office for the Americas (PAHO) celebrated the news with announcements titled, in part, “Bye, bye measles!”

But now—after a global resurgence of the highly infectious viral illness, spurred partly by misinformation and vocal anti-vaccine advocates—both of those achievements are close to being undone.

Massive outbreaks of measles ignited late last September in New York. The disease has continued to spread in flare-ups around the country, sickening a total of 1,215 people since the start of 2019. This week, the CDC reported 12 new cases from the week before. Experts expect the weekly case counts will rise with the start of school—and they’re bracing for a stinging defeat.

"We're embarrassed. We're chagrined," infectious disease experts Dr. William Schaffner from Vanderbilt University told CNN.

Messonnier echoed the feeling, telling CNN: "It certainly is incredibly frustrating and upsetting to the public health community that we may lose measles elimination status, because we do have a safe and effective vaccine.”

The US wouldn’t be alone in its humiliating defeat. Earlier this month, the WHO determined that the UK had lost its measles-elimination status , which it had won only in 2017.

“Losing our ‘measles-free’ status is a stark reminder of how important it is that every eligible person gets vaccinated,” Dr. Mary Ramsay, head of immunization at Public Health England, said in a tweeted statement.

Schaffner and others in the public health community blame vaccine misinformation as well as themselves for the losses, saying that they were not fast and effective enough to protect the public. "I think this was not our finest hour," Schaffner said.

In a statement released today, Wednesday, August 28, WHO Director-General Dr Tedros Adhanom Ghebreyesus addressed the problem of vaccine misinformation directly.

“Misinformation about vaccines is as contagious and dangerous as the diseases it helps to spread,” he said in the statement. While he urged governments to strengthen health services, he called upon social media platforms and the private sector in general to help in the fight. “I call upon them to do more to filter out misinformation and inaccuracies that prevent people from achieving health and well-being.”

In April, the World Health Organization reported that worldwide cases of measles in the first three months of 2019 were 300% higher than those in the first three months of 2018. In 2017, the most recent year for which there’s complete data, measles caused close to 110,000 deaths.

This post has been updated to correct a typo. There were close to 110,000 deaths from measles in 2017, not 11,000.