Do you remember when measles was eliminated in the United States?

You probably should.

It wasn’t that long ago…

When Measles Was Eliminated in the United States

After several years of declining numbers of measles outbreaks in the United States, the endemic spread of measles was declared eliminated in March 2000.

“The data indicated that, during 1997–1999, measles incidence has remained low (<0.5 cases per 1,000,000 population) and that most states and 99% of counties reported no measles cases. In addition, measles surveillance was sensitive enough to consistently detect imported cases, isolated cases, and small outbreaks. Evidence of high population immunity included coverage of >90% with the first dose of measles vaccine in children aged 19–35 months since 1996 and 98% coverage among children entering school. In 48 states and the District of Columbia, a second dose of measles vaccine is required for school entry. A national serosurvey indicated that 93% of persons aged >6 years have antibody to measles.”

Measles — United States, 1999

What did that mean?

It is easy to understand when you note that we still had 86 cases of measles in the United States that year.

So, measles wasn’t gone yet. It was just that most cases were imported from outside the country. Only imported strains of the measles virus were causing outbreaks.

“The end of endemic measles transmission in the United States has both domestic and international importance. Domestically, the absence of endemic exposure to measles means few persons in the United States will be infected and risk complications of measles. This decreased risk of exposure provides protection to groups not protected directly by vaccination: children too young for routine vaccination; the few persons who, although vaccinated, are not protected, primarily from failure to mount an adequate response to vaccine; persons for whom vaccine is contraindicated (e.g., those with immunodeficiency); and persons who choose not to be vaccinated.”

Wharton on Measles Elimination in the United States

Unfortunately, the “choose not to be vaccinated” group might be endagering our claim to have eliminated measles.

Is Measles Still Eliminated in the United States?

As we break more and more measles records this year, it would be easy to just say that the endemic spread of measles is no longer eliminated in the United States.

“Endemic measles transmission is the existence of any continuous indigenous chain of transmission of measles virus that persists for >1 year in any defined geographic area (e.g., the United States).”

Orenstein on Defining and Assessing Measles Elimination Goals

Still, when you look at the numbers, technically, measles isn’t yet spreading endemically in the United States.

We are getting close though.

The outbreaks in Rockland County and Brooklyn started in September and October 2018. If they aren’t stopped soon, will it be easier to make a case that measles is no longer eliminated in the United States?

“Outbreaks in New York City and Rockland County, New York have continued for nearly 8 months. If these outbreaks continue through summer and fall, the United States may lose its measles elimination status.”

U.S. measles cases in first five months of 2019 surpass total cases per year for past 25 years

It sounds like it.

One thing to consider though, after an unvaccinated visitor introduced measles to Brooklyn from Israel back in October, measles has been reintroduced into the community at least seven other times! This includes travelers from Israel, UK, and Ukraine.

So the outbreak isn’t necessarily a “continuous indigenous chain of transmission of measles virus.”

It is multiple chains in the same community.

“There have been additional cases of measles from international travelers to Rockland, exposing more people to measles.”

2018 – 2019 Measles Outbreak in Rockland County

The same thing has happened in Rockland County after the initial importation from Israel in September.

Measles Elimination Criteria

Does that matter?

It likely should, but let’s also look at how we do with other criteria that are often used to assess the absence of the endemic spread of measles:

• Few measles cases/low measles incidence – we will have the most cases in 2019 since 1992, but most cases are clustered in just a few big outbreaks
• The duration of outbreaks is short – outbreaks are getting longer and harder to contain, but part of the problem is the global rise in measles and the reintroduction of measles into existing outbreaks
• Most cases are associated with international importation – still very true
• No endemic measles virus strain – outbreaks this year have been associated with strains that are commonly seen in Ukraine, the Philippines, and a few other areas
• Long periods with no unknown-source cases – most cases are linked to international travel
• High population immunity – except for pockets of susceptibles, folks who intentionally don’t vaccinate their kids or get themselves vaccinated, we do have high population immunity
• Low levels of transmission from reported cases – in most outbreaks, that it is still true, unfortunately, there are more outbreaks this year
• Adequate measles surveillance system – definitely true

What is the best argument that the endemic spread of measles has still been eliminated in the United States?

“A small number of cases have occurred outside of these neighborhoods but have, to date, not resulted in sustained transmission of measles.”

Measles Cases Rise to 466 Including in Two Unvaccinated Children Spending Time in Areas with Measles Activity

Even where there are big outbreaks, measles isn’t spreading outside of very specific communities of intentionally unvaccinated children and adults.

And that’s because most people are vaccinated and protected and aren’t letting measles spread endemically!

Losing Measles Elimination Status

If we did lose our status of having eliminated measles, we wouldn’t be the first.

“As of 30 June 2018, measles transmission in Venezuela has been ongoing for over one year. Therefore, endemic transmission of measles is considered to have been reestablished in Venezuela.”

Fourth ad hoc Meeting of the Technical Advisory Group (TAG) on Vaccine-preventable Diseases

Tragically, since their outbreaks began a few years ago, there have been nearly 10,000 cases and at least 78 deaths. Cases have also spread to many other countries in South America.

Venezuela isn’t the only country where we have seen the return of measles though.

In 2017, the European regional verification commission verified the reestablishment of the endemic spread of measles in the Russian Federation and in Germany.

“Countries in all six WHO regions have adopted goals for measles elimination by 2020.”

Progress Toward Regional Measles Elimination — Worldwide, 2000–2017

Surprisingly, some other countries in Europe, like Belgium, France, and Italy, never eliminated measles.

What’s next?

Hopefully, instead of a new normal, the rise in cases gets us back on track to eliminating and one day eradicating measles.

More on When Measles Was Eliminated in the United States

• Who’s Getting Measles?
• Why Haven’t We Eradicated Measles Already?
• Who Is ‘Patient Zero’ in the 2019 Measles Outbreaks?
• MMWR – Measles — United States, 1999
• Measles Elimination in the United States
• Defining and assessing measles elimination goals.
• CDC – U.S. measles cases in first five months of 2019 surpass total cases per year for past 25 years
• CDC – Most Measles Cases in 25 Years: Is This the End of Measles Elimination in the United States?
• ECDC – Who is at risk for measles in the EU/EEA?
• WHO – Fourth ad hoc Meeting of the Technical Advisory Group (TAG) on Vaccine-preventable Diseases
• WHO – Eliminating measles and rubella
• CDC – Progress Toward Regional Measles Elimination — Worldwide, 2000–2017
• Measles Cases Rise to 466 Including in Two Unvaccinated Children Spending Time in Areas with Measles Activity
• 2018 – 2019 Measles Outbreak in Rockland County
• Measles Elimination in the Americas
• Measles cases are up nearly 300% from last year. This is a global crisis.