Measles was declared 'eliminated' in the U.S. over 20 years ago. Is the country close to having that status revoked?

Three months into 2025, the U.S. has surpassed the total number of measles cases reported in all of 2024. Measles is one of the most contagious diseases in the world and can lead to serious health complications, especially in children under 5 who aren’t vaccinated.

A Yahoo News count using data from state and county departments of health puts the total tally of reported cases in the U.S. at 380 as of March 21, exceeding last year's 285.

The rise in cases is concentrated in a multistate outbreak that started in West Texas and has spilled over into parts of New Mexico and Oklahoma.

West Texas has the bulk of cases, which increased to 309 on Friday. A public health official there said this outbreak could last for a year.

“This is going to be a large outbreak, and we are still on the side where we are increasing the number of cases,” Katherine Wells, director of Lubbock Public Health, said at a Tuesday press conference. “I’m really thinking this is going to be a year long.”

“I just think, it being so rural now, multistate — it’s just going to take a lot more boots on the ground, a lot more work to get things under control. It’s not an isolated population,” Wells added.

The U.S. achieved measles elimination status in 2000 after a year of no endemic spread of measles. Then in 2016, the continents of North and South America reached elimination status.

However, a recent World Health Organization report states that North America’s “eliminated” status is at risk. Health officials say if there is a continuous chain of measles transmission in a specified area for at least a year, then the U.S. would lose its elimination status. “Independent regional commissions verify a country’s elimination status,” according to the Centers for Disease Control and Prevention.

But it’s not the first time the U.S. has been warned.

In 2019, the U.S. was at risk of losing its elimination status after measles outbreaks were sustained for several months in under-vaccinated communities in New York state. The U.S. ultimately kept its status after an educational outreach campaign helped community members get vaccinated, along with constraints set in place that banned unvaccinated children from physically attending school.

“The combination of all of those activities over time brought that outbreak to a close,” Dr. William Schaffner, professor of infectious diseases at Vanderbilt University School of Medicine, told Yahoo News.

Yahoo News spoke with Schaffner about the current measles outbreak and how it can come to an end. (Some answers have been lightly edited for length and clarity.)

What are health officials doing to help stop the spread of measles in West Texas?

The key to preventing measles is vaccination. In West Texas, this measles outbreak is occurring in a population of very under-vaccinated, conservative Mennonite people who have relied on some kind of “natural medicines.” The behavioral psychologists have instructed us that when they have very firmly held beliefs, and they encounter information that's contrary to those beliefs, what they do is double down on the belief.

Even doctors that are there caring for these patients day in and day out have not been persuasive in getting many people, some for sure, to change their minds and accept the vaccine. But everything is being done in that regard, trying to reach out to this population in a friendly and very respectful fashion to get them to try to accept vaccination. Education, consultation, comforting, reassurance — all of those things are happening and I think are being met with some limited success.

If the rate of acceptance of vaccination is low, and these people interact, even though they are widespread in a rural area, they can keep coming into contact with each other. So measles can keep smoldering in this population.

What is considered an outbreak, and how does it end?

An outbreak is an occurrence of illness in a population in which it didn't occur before. In this [West Texas] instance, it's a very well-defined population. So as it continues in this population, it would be considered an outbreak.

An outbreak ends when there are no more cases, and you usually wait at least two incubation periods [which is about 40 or 50 days]. An incubation period is the period of time after a susceptible person has been exposed, and then the disease occurs. In other words, the virus is in the body, but it hasn't made you sick yet. And with measles, that can be quite prolonged; it's usually 10 to 20 days. It can go up a little bit longer than that.

In a population that is spread out [in a rural area] and is rather wary of authority, you want to be very sure. We would probably wait a little longer because there are undoubtedly cases of measles that are occurring not being seen by health care providers, and thus families don't want them reported.

You really want to be careful and give it enough time and have security in your surveillance to make sure … it's really over before you declare the outbreak finished.

Should we be worried about the measles outbreak in West Texas?

One of the good things that's really quite evident is that this measles outbreak, as with other measles outbreaks that have occurred in the United States, is not spreading to the surrounding general population. And that's because that population is either the older people, who experienced real measles, or from middle age on down, who have been pretty solidly vaccinated.

Both of those — the disease itself and its recovery and vaccination — provide very solid, durable, long-term protection against measles. This is essentially a measles outbreak that is confined to this high-risk [Mennonite] population.

Could eliminated status be threatened, and at what point?

Elimination status means that you do not have sustained transmission within your confined area, your country, whatever it is. In other words, if measles is imported into your country and it affects some people who are unvaccinated, how many successive generations of spread does it take?

In other words, there's one person who gets infected who infects another, that's one generation. The second person infects a third, that's the second generation. Almost always in the United States, we have been able to end the outbreaks, bring them to a close very quickly, because the general population is well protected, and you can go into that affected population and quickly persuade people to be vaccinated.

But if you have a population [like in West Texas] … where there are several generations of transmission, if that continues, then you might lose your elimination status.

But it's quite clear that everybody has to keep vaccinating because there's still plenty of measles in the world. If you slack off on vaccination, you build up susceptible people, and pretty soon, measles will be imported back into your country and start spreading again.

You have to maintain a rigorous vaccination program. For measles, you strive for vaccination rates that approach, and maybe even exceed, 95% because it's the most contagious virus we know.