In 1980, measles caused 2.6 million deaths worldwide. Widespread use of the two-shot measles vaccine over the past four decades changed that. By 2000, routine immunization was preventing 80 million cases of the infection each year.

That year, the World Health Organization declared measles “eliminated” in the United States. There was no longer continuous circulation of the virus here. All measles cases could be traced to unvaccinated people catching the disease outside the country or infected people from abroad bringing it in.

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Now, that is changing.

The United States has recorded 1,241 cases of measles so far this year. (It used to have fewer than 100 each year). While they’ve occurred in 31 states, more than three-quarters have been in New York, where a smoldering outbreak has been underway since last October. If a country has a continuous chain of measles transmission lasting more than a year, the disease is no longer considered “eliminated.” If new cases linked to the New York outbreak occur after Tuesday, that will be the situation here.

Things are worse elsewhere. Worldwide, measles cases doubled from 2017 to 2018. Through July, there have been three times as many cases as in the same period last year.

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In recent years, experts have tried many ways to convince vaccine-refusers the unwisdom of their choice. It’s now time for a plea rather than an argument. Anti-vaxxers, please make an exception for measles vaccine, because measles is a special case. Here’s why.

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Measles is caused by a type of Morbillivirus; similar ones attack cats, cattle, seals and other animals. A common feature is the ease of transmission — a quality captured by what biologists call the “basic reproductive number” (denoted R0). It’s the number of new cases that occurs when an infected person circulates among susceptible people.

R0 is an average that depends on lots of things, including human behavior and population density. The biggest driver, however, is the bug itself. Measles has an R0 of 12 to 18 — so high that the infection is often described as the most contagious disease in man. In comparison, R0 for the 1918 pandemic influenza virus was 3.8. For smallpox, it is 4.5; for polio, 6; for SARS, 3.5.

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The virus spreads through “respiratory aerosols,” which can hang in the air for hours. A study of measles transmission on airplane flights found that the average distance between the person with the disease and the person who came down with it was six rows. In one case, it was 17 rows.

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While measles is in a class of its own when it comes to contagiousness, luckily that’s not true for mortality. In the 1950s, the United States averaged 440 measles deaths a year — a fraction of 1 percent of total cases. In poor countries, it was a different story. Epidemics occurred every two years, infecting all children born since the last one and killing 3 to 5 percent of them.

Luckily, the vaccine protects 97 percent of the time after two doses. It’s so good that measles is a candidate for global eradication, a feat achieved only with smallpox. It’s no coincidence that the only eradicated animal disease is rinderpest — cattle measles — thanks to a vaccine.

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None of this would matter if the measles vaccine wasn’t safe. But it is. The most common serious reaction — a seizure caused by fever — occurs in 3 out of every 10,000 shots. It also doesn’t cause autism, as innumerable studies have proved, although vaccine skeptics who think the question is still open are unlikely to ever be convinced.

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Fortunately for them (but not us), their children are protected by “herd immunity,” which kicks in when about 95 percent of the population has been vaccinated. But there’s a problem. Pockets of the population — immunocompromised children, members of certain religious groups — are loaded with susceptible members. Immunity in the rest of us has to be higher than the herd threshold to keep the virus from eventually finding them.

That’s where we are today. Every immunized child plays a mathematical role in protecting kids who can’t protect themselves. But you may ask: Isn’t this just statistics without a human face?

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Unfortunately, no.

In August, a 43-year-old Israeli flight attendant died five months after going into a coma caused by measles encephalitis. It’s believed she contracted the infection on a flight from New York, where there was an ongoing outbreak. She had been vaccinated at a time when children got only one shot and wasn’t fully immune.

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Her death angered Grabowsky.

In the 1990s, he worked to push measles vaccine coverage above 80 percent in seven African countries. After five years, it was up to 91 percent, with no confirmed measles deaths in 2000 (Undoubtedly, there were a few.) While the action of millions made the achievement possible, it was the action of one person that Grabowsky thought of when he heard about the flight attendant.

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“Vaccination is one of the purest markers of individual actions having public consequences,” he told me. “It’s outrageous that somebody neglected their public responsibility and it led to a stranger’s death.”

Now 63 and retired from the Public Health Service at the rank of captain, he has come to view vaccination as part of the social contract. “It’s like paying taxes to build bridges we’ll never drive over and paying teachers who’ll never teach our children. It’s part of citizenship.”

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It’s true that if you don’t vaccinate your child against measles you probably won’t pay a price for it. But eventually somebody will.

So, here’s the request: Vaccinate your child for that person.