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Measles cases rose 79% globally last year, WHO says. Experts explain why.

Thousands of schools at risk of measles outbreak
Thousands of U.S. schools at risk of measles outbreak, data shows 02:18

The World Health Organization is warning about the rapid spread of measles around the world, noting a 79% increase from 2022, with more than 306,000 cases reported last year.

In a news conference Tuesday, the U.N. health agency said it did not yet have an overview of measles deaths last year but expects increases in fatalities from the disease.

"In 2022, the number of deaths increased by 43%, according to our models, to more than 130,000 deaths occurring from measles," WHO technical adviser Natasha Crowcroft said.

Given the growing case numbers, "we would anticipate an increase in deaths in 2023 as well," Crowcroft added.

The WHO announcement comes as a concerning rise in measles cases at a Florida school district is putting people there on high alert.

On Friday, Broward County Public Schools announced that there was one confirmed case reported at Manatee Bay Elementary School. The next day, BCPS announced that three additional cases were reported overnight, bringing the total to four.

Health experts say these cases could just be the beginning. While measles — a highly contagious and potentially deadly virus that causes a tell-tale rash — was officially declared eradicated in the U.S. more than 20 years ago, new outbreaks of the disease are popping up. Declining vaccination rates are jeopardizing herd immunity and increasing the risk of outbreaks.

"The way this viral illness spreads, we foresee that the number of unvaccinated children, the immune-compromised, we will start to see an increase in those numbers definitely," Dr. Pallavi Aneja, the program director of Internal Medicine Residency at HCA FL Northwest and Westside Hospitals, told CBS News Miami.

Data across the country also shows parents have reason to be concerned.  

Examining data from tens of thousands of public and private schools in 19 states and communities that make the information available to parents and the public, a CBS News investigation last month identified at least 8,500 schools where measles vaccination rates among kindergartners are below the 95% threshold that the CDC identifies as crucial for protecting a community from measles.

The drop in school-age vaccination rates is alarming scientists and doctors across the country. In January, a cluster of measles cases were identified in Philadelphia, and 82 children in Ohio contracted measles in 2022.

"I think it's concerning to me as a human being," Matt Ferrari, Penn State University biologist and infectious disease researcher, previously told CBS News. "It also has a population-level consequence. The more individuals that are around who are unvaccinated, the more potential there is for disease to spread and to establish transmission that will give rise to outbreaks that will stick around for a long time."  

Winning hearts and minds over vaccines 09:50

Looking ahead, 2024 is going to be "very challenging," the WHO's Crowcroft added. 

"One of the ways we predict what's going to happen in terms of outbreaks and cases is looking at the distribution of unimmunized children," she said. "We can see from data that's produced with WHO data by the U.S. CDC that more than half of all the countries in the world will be at high or very high risk of outbreaks by the end of this year."

–Stephen Stock, Aparna Zalani, Chris Hacker, Jose Sanchez and staff from CBS Miami and CBS Philadelphia contributed to this report. 

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