Updated at 6:50 p.m. ET

This year's measles outbreak is the largest since the 1990s. The Centers for Disease Control and Prevention announced Monday that 75 more measles cases were confirmed last week in 23 states, bringing the U.S. total to 839 so far this year.

The outbreak from 1989 through 1991 was much larger than today's, with more than 27,000 cases in 1990 alone. But the conditions that lead to that outbreak and what it took to end it are dramatically different from the ones the U.S. is seeing today.

The bulk of cases today are concentrated in New York state. As of Monday,New York City alone reports 498 cases, with 34 people hospitalized, since the outbreak began last September.

In New York state, public health authorities attribute the outbreak to anti-vaccination sentiments among a small subgroup of religious Orthodox Jewish residents among whom the virus has spread. The outbreak in the early 1990s hit poor black and Latino communities the hardest, in Central Brooklyn, upper Manhattan and the South Bronx.

The outbreak in New York City took off in the spring of 1990. And once the public health response got underway, parents got on board.

"Children were dying," says Dr. Irwin Redlener, who founded the Children's Health Fund to bring health care to New York City's poorest areas. "It was like all hands on deck. The city, the not-for-profit organizations, were all focused on the same mission with the enthusiasm of parents."

According to news reports from the time, criminal courts had to halt proceedings when inmates at the Rikers Island jail got sick. There were outbreaks on college campuses and in homeless shelters. One defunct hotel turned city shelter that Redlener visited was so overcrowded that it was an outbreak waiting to happen, he says.

"The conditions in the hotel and the lack of access to care — you have basically set up a scenario that is very conducive to the spread of a disease like measles," says Redlener.

The outbreak continued that fall, into the next year and through the summer of 1991. By the time it was over, there were more than 5,000 measles cases in the city and at least 21 deaths. It wasn't just in New York City either; starting in 1989, Chicago, Los Angeles, Houston and Philadelphia were experiencing large outbreaks as well. From 1989 through 1991, more than 55,000 were sickened and more than 100 people died across the United States, the highest numbers since the early 1970s, according to data from the CDC.

Public health historians partially attribute the outbreak to budget cuts during President Ronald Reagan's administration that affected federal funds directed toward immunization and public health initiatives.

"There was just less White House support for childhood immunization," says Elena Conis, an associate professor at the University of California, Berkeley, where she specializes in medical history.

Immunization rates peaked in the early 1980s because of investment during the prior administration of President Jimmy Carter. There was just one death attributed to measles in 1984, the lowest number ever recorded by the CDC. But as federal investment didn't keep up with inflation or with increases in the cost of the vaccine, immunization levels crept downward, particularly in areas where parents couldn't afford vaccinations.

Some federal funds that had been earmarked for immunizations in the past were instead given in lump sums to states, Conis says. And according to Conis, there was a third issue.

"We had a health care system that simply wasn't designed to serve low-income kids living in cities who were more reliant on public clinics, which weren't necessarily open all the time ... or were few and far between," Conis says.

By the time the outbreak hit in 1990, the CDC estimated that about half of all inner-city toddlers in New York City had not been vaccinated by their second birthday.

"Over the past years of tight budgets, the immunization programs have been eroded. ... The results have been predictable," Rep. Henry Waxman of California said at a 1991 hearing about the nationwide outbreaks. "The problem is clear to see. Vaccination programs are limited. Clinics are inaccessible. Appointments are required, and waiting lists have also grown."

Even worse, without access to preventive care, kids who got really sick with measles ended up in the hospital.

"We saw ... a lot of kids with measles and pneumonia, measles and croup, measles and acute encephalitis," says Dr. Joel Forman, who was just starting his pediatric residency at Mount Sinai Hospital in New York City in the summer 1990. Years later, one of Forman's patients died from an extremely rare complication from measles called subacute sclerosing panencephalitis.

"When he first was sick of measles, he was 7 months — I remember that," Forman says. "He recovered uneventfully and only presented years later with a lethal complication."

By the summer of 1991, New York officials redoubled their efforts, with Mayor David Dinkins and Gov. Mario Cuomo working in concert. Measles messages were flashed across the giant Sony computer screen in Times Square. Buses outfitted as mobile health clinics offered free immunizations. One immunization drive featured Michelangelo from the Teenage Mutant Ninja Turtles, who emerged from a sewer at the South Street Seaport to encourage kids to get the vaccine. Shots were given to kids at parks, beaches and outdoor concerts, including one featuring Latin jazz icon Tito Puente. The outbreak eventually petered out.

On the federal level, things were changing too. In 1993, newly elected President Bill Clinton pledged to raise childhood immunization rates. That year, Congress created the Vaccines for Children program, which funded vaccinations for children whose parents couldn't afford them, and federal funding increased sevenfold from $37 million in 1990 to $261 million in 1995.

Measles vaccination rates climbed above 90%, where they've remained in most places. New York became the first state to require a measles booster shot, which is now required across the country and is said by the CDC to increase the effectiveness of the vaccine from 93% to 97%.

Today's measles outbreak in New York is far smaller than the one in the 1990s. And the reasons behind it are very different.

"Then, it was people who couldn't get access to health care," Redlener says. "Now it's this cultlike atmosphere of people who are refusing to immunize."

Since last fall when the outbreak began, city health officials say, more than 20,000 doses of the measles, mumps and rubella vaccine have been administered to children in Brooklyn neighborhoods. City health officials have met with community leaders, published ads in community papers, sent out robocalls and hosted conference calls with doctors.

Still, they're facing a small but mobilized subgroup of the ultra-Orthodox community that opposes vaccines and has links to the larger, secular anti-vaccination movement. This has hindered the city's ability to stop the spread of measles so far, said Dr. Demetre Daskalakis, deputy health commissioner, at an April 17 meeting of the city's Board of Health.

He spoke of parents not seeking medical care for sick kids or intentionally exposing children to the measles virus at "measles parties," and of the spread of misinformation about the vaccine.

"There's a lot of things we're working against," he said.

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