The number of measles cases reported in the United States has risen to 839, according to the U.S. Centers for Disease Control and Prevention.

That's up from 764 cases reported last week, when officials said the outbreak had reached a level not seen in the U.S. in 25 years.

Measles cases have been reported in 23 states this year. But New York has the biggest outbreak, accounting for almost 700, or more than 80 percent, of the cases nationwide.

Some states are working to limit the reasons parents can cite for not vaccinating their children. Connecticut lawmakers are contemplating removing that state's religious exemption. And last Friday, Washington's governor signed a law that says parents with children heading to daycare or school will no longer be able to claim personal or philosophical objections to the measles, mumps and rubella vaccine.

During a news conference Friday, Washington Gov. Jay Inslee said, "We believe in science. And we love our children. And that is why in Washington state, we are against measles."

Lawmakers in Maine and Oregon are considering similar legislation.

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