It's been fifty years since the United States approved a vaccine to prevent measles — and more than a decade since the disease was declared eliminated in the country. But now, the rate of measles is once again on the rise: a new report from the US Centers for Disease Control and Prevention (CDC) has concluded that 2013 saw measles infections increase to three times the typical number.

A total of 175 confirmed measles cases have been diagnosed so far this year, most of them clustered in one of nine outbreaks that occurred across the country. And of those diagnoses, a whopping 98 percent were in patients who hadn't been vaccinated. "This is isn't the failure of a vaccine; it's the failure to vaccinate," Thomas Frieden, the CDC's director, told reporters at a press conference earlier today.

"This is isn't the failure of a vaccine; it's the failure to vaccinate."

Even after measles vaccines became commonplace in the US, the country still saw "imported" cases of measles on an annual basis — largely international visitors infected with the virus. In pockets of the country with low vaccination rates, however, that poses a serious threat: earlier this year, several unvaccinated members of a Texas mega-church became infected with measles after a local contracted measles overseas. According to the CDC, nearly every measles infection this past year can be linked back to international travel. "A measles outbreak anywhere is a risk everywhere," Frieden said. "The steady arrival of measles in the United States is a constant reminder that deadly diseases are testing our health security every day."