The record-large measles outbreaks occurring across 22 states continue to grow, with a total of 704 cases through Friday, according to new data released Monday by the Centers for Disease Control and Prevention.

Why it matters: U.S. measles outbreaks so far this year have eclipsed all other outbreaks in any year since the virus was declared eradicated in the country in 2000. The total number of cases has been dominated by three outbreaks in particular, including a large outbreak in Washington state, two ongoing outbreaks in New York and an ongoing outbreak in California.

The New York outbreaks have been the largest individual outbreaks on record since 2000, a CDC official told reporters on a press call.

The big picture: Measles is a preventable, sometimes deadly illness against which a safe and effective vaccine exists. The U.S. outbreaks have been touched off by travelers coming into the U.S. from regions where measles outbreaks are ongoing. The disease is then spread in regions where there was not sufficiently high levels of immunization.

Countries that have resulted in the accidental importation of measles cases into the U.S. include Ukraine, Israel and the Philippines.

What they're saying: CDC director Robert Redfield emphasized the contagiousness of measles, stating that if someone who has measles enters a room of 10 unvaccinated people, 9 of them would get the illness.

Health officials warned on Monday that measles is not a harmless childhood illness and it can be deadly.

From 2001 to 2013, 28% of children younger than 5 years old who had measles had to be treated in a hospital, CDC spokesperson Jason McDonald told Axios last week, referring to relatively small outbreaks related to measles patients who traveled to the U.S. from areas where the disease is still active.

"Some children develop pneumonia, a serious lung infection, or lifelong brain damage," he said.

Details: The national average vaccination coverage in kindergarten children — 94.3% for 2 doses of the measles, mumps and rubella vaccine for the 2017–2018 school year — is at a level consistent with the "herd immunity" necessary to prevent a nationwide outbreak. However, pockets of community resistance to the vaccine, including in ultra-Orthodox Jewish communities in New York City, are allowing the virus to make inroads, officials said.

"Vaccine preventable diseases belong in the history books, not in our emergency rooms," Health and Human Services Secretary Alex Azar told reporters.

The CDC is urging individuals who are unsure of their vaccination status or who have questions about the safety of the vaccine to contact their health care provider.

What's next: "We should expect to see additional cases associated with this outbreak this year," said Nancy Messonnier, director of CDC’s National Center for Immunization and Respiratory Diseases.

Messonnier added that the measles outbreak in New York could be contained if officials work together to increase vaccination rates and counter disinformation raising concerns about the safety of the vaccine. "Once measles is in an undervaccinated community, it is difficult to control the disease," she said.

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